"I still don't know what to wear for office casual attire."
Do you find yourself stopping in front of your closet every morning, still grappling with such doubts?
The period from the end of August through September, in particular, when the lingering summer heat continues, is a challenging time when we need to cope with the heat while also being mindful of the autumn season.

A male attendant from Isetan Shinjuku will explain the basics of office casual attire in an easy-to-understand way.
Even with the same item, paying attention to the material and design can make it appear more elegant and sophisticated.

This article covers essential rules, examples of what to avoid, item selection, seasonal transitions, and tips for creating versatile outfits— all for businessmen, especially those in their 30s and 40s.

By the time you finish reading, you should have a clearer idea of what constitutes appropriate office casual attire for your workplace.

Basic rules and examples of what not to do in business casual attire.

"Office casual" refers to attire that incorporates casual elements while maintaining a professional and polished appearance suitable for a business setting. Even for those working indoors, overly casual attire is not advisable.
While it's essential to adhere to company regulations and workplace culture, aim for an outfit that is well-received by those around you and gives a clean, polished impression by skillfully incorporating casual items.

■ The three main principles of office casual attire

No matter how expensive the items you have, if the following three points are not met, it will create a "disappointing impression."
The "clean and neat" office casual attire proposed by Mitsukoshi Isetan is not simply about wearing freshly laundered clothes. It's important that not only are the clothes in good condition, but also that they fit well and give a neat overall appearance, conveying sincerity, elegance, and trustworthiness. Be mindful of your overall appearance, including your hairstyle, nails, and shoes, to ensure you look clean and presentable.

principle	point
Cleanliness	Avoid wrinkles, pilling, yellowing, and stains. The overall look should be neat and tidy, including the color scheme and texture.
Size	Too big or too small is a no-no. It's important that the shoulder width, length, and sleeve length are a good fit.
silhouette	The overall look should be neither too slim nor too loose. Pay attention to the balance between the top and bottom.

■ It's also important to adapt to the dress code trends of your workplace.

Office casual attire can vary depending on the workplace and industry. Adjusting your attire to suit your workplace and daily schedule is key to avoiding fashion mistakes.
For example, when negotiating with clients or customers, a relatively neat and tidy appearance is required. On the other hand, while there tends to be more freedom in what you wear while working in the office, the common requirement is that you should not look sloppy in any workplace.

type	Guidelines for the workplace (scene)	Clothing guidelines
A (closer to a suit)	Important business meetings, outside sales calls, etc.	Jacket recommended. Shirt and slacks are the basic attire.
B (Standard)	Internal meetings, etc.	A jacket is acceptable depending on the situation. Chinos or a knit sweater are also fine.
C (Less casual)	Office work, teleworking, etc.	There's a high degree of freedom. However, you need to pay attention to cleanliness and size.

■Examples of "office casual" attire to avoid

If you lean too far towards the "casual" side of "office casual," it can give the impression that you're not suitable for the workplace.
In particular, avoid the following items and styles of dress:


What's important in office casual attire isn't flashiness, but a neat and tidy appearance . Just by following this basic rule, you can make a big difference in the impression you give.

Examples of what NOT to do	Problem	alternative
The jacket's shoulders are drooping.	The whole thing looks sloppy.	Prioritize choosing something that fits your shoulder width.
The hems of the pants are baggy.	The whole thing looks loose.	Check the length when purchasing and have the hem altered if necessary.
Light clothing items such as printed T-shirts, shorts, and sandals.	It's too casual and can easily come across as "slacking off" in the workplace.	Wear a plain, high-quality T-shirt as an undershirt; keep the amount of exposed skin around your ankles to a minimum, as this is appropriate for a business setting.
Distressed denim	Scratches and discoloration detract from a clean appearance.	I'll go with dark-colored straight-leg jeans.
Worn-out sneakers	Dirt and yellowing can detract from a clean appearance.	Regularly maintain or replace it.

A guide to choosing "office casual" attire, item by item!

① Jackets: How to choose between a set-up and individual pieces

A jacket is a basic item that adds a touch of sophistication and elegance to office casual attire.
Simply throwing on one of these pieces will make your whole look more polished, making it easier to handle unexpected visitors or business meetings.

■ Setup

Since the top and bottom are made of the same material, it's easy to put together an outfit and less likely to go wrong, which is a major advantage.
It's easy to create a cohesive look overall, so it's reassuring to have at least one of these in your wardrobe.

■Single Jacket

It's easy to pair with slacks or chinos, and its strength lies in its versatility, as you can freely combine colors and materials for the top and bottom. It's also a great item to use when you want to create a slightly lighter impression.
When choosing a jacket, the fit around the shoulders and the overall silhouette are crucial. As a basic rule, make sure the shoulders don't droop too much, and also check the length of the jacket and sleeves.

② How to choose tops and how to use innerwear

When choosing tops for "office casual" attire, the basic principle is to be mindful of the different levels of formality each item conveys. For businessmen in their 30s and 40s, as well as for general office casual wear, a good balance can be achieved by focusing on shirts and polo shirts, and incorporating knitwear or T-shirts depending on the day's schedule and the atmosphere of the workplace.

The following order can help you understand the "level of tension":


Shirts easily give off a neat and tidy impression, while polo shirts create a moderately relaxed look.
High-gauge knitwear is easy to wear during transitional seasons, while T-shirts are more casual, so it's safest to wear them mainly as an inner layer under a jacket.

■Tips on how to wear a shirt

When wearing a shirt without a tie, it's important to unbutton the top button and straighten the collar.
A sloppy collar can easily detract from a clean and neat appearance, so it's best to maintain its shape by using a button-down collar or ironing it.
When wearing a white shirt, it's also important to take precautions against it being see-through .
Choosing a beige or gray U-neck or V-neck inner layer will prevent it from being see-through and give you a neater look.

③ Choose bottoms based on material and silhouette.

Even if your top and jacket are well-chosen, if the material and length of your pants don't match, the whole outfit can look sloppy or even careless.
First, it's important to choose a material that suits the occasion and to adjust the size and silhouette .

material	Scene guidelines	point
Wool slacks (lightweight)	Meetings, conferences, and business negotiations with clients.	It's suitable for occasions where you want to project a polished image, and is especially easy to use from September onwards.
Cotton Chino Pants	Daily office work, internal operations	When paired with a jacket, it creates a moderately polished look.
Functional fabric pants	Long hours of desk work, business trips	It's important to choose something that's easy to move in and handle, not too casual, and with a good texture.
denim	Only for workplaces where casual attire is acceptable.	Dark, straight hair is the basic style. Distressed hair is not allowed.

■Basics of Size and Silhouette

For bottoms, it's important that the hems aren't too long and that they flatter the leg line.

• Silhouette : A straight to tapered silhouette looks neat and is easy to wear for office casual occasions.

- Hem length : The ideal length is somewhere between the ankle and the top of the foot.

④ Footwear: How to choose leather shoes and sneakers

When choosing footwear for office casual attire, the basic rule is to select something that matches the overall style of your outfit and your plans for the day.
On days when you want to look polished, leather shoes are a good choice, while leather sneakers are also an option in workplaces with more flexibility.

shoes	Matching styles	point
Derby (open lacing)	Setup and business negotiation scene	It makes it easier to create a more polished impression. I want to make sure everything is in order, including the leather care.
Loafers (leather/suede)	Jacket + Slacks	Highly versatile and a staple of office casual wear. Suede becomes easier to incorporate into your wardrobe from September onwards.
Leather sneakers	Casual office	The basic principle is simplicity and cleanliness. Avoid thick soles and overly sporty designs.

Whether it's leather shoes or sneakers, choosing them based not only on design but also on how you'll maintain them on a daily basis is key to creating a polished impression.
► [Read related articles] [2026 Business Sneakers] 6 Recommended Shoe Brands You'll Want Right Now

⑤ Use accessories and color scheme to refine the overall impression.

Office casual attire is influenced not only by the clothes themselves, but also by the choice of colors and accessories. Rather than adding flashy items, choosing accessories that blend well with your outfit and create a cohesive overall look naturally leads to a sophisticated impression.

A guide to choosing office casual items for each season.

When it comes to office casual attire, it's not just about matching the temperature; it's also about creating a sophisticated look. We recommend using comfortable materials and seasonal colors to effortlessly achieve a refined impression.
Especially during seasonal changes, paying attention to the balance between comfort and appearance will create a naturally refined look.

■ Guidelines for choosing according to the season

season	Key points of the material	Points to consider when choosing a color
Spring (March to May)	Lightweight and soft cotton or thin material (cotton-linen blend)	Light navy, blue, beige
Early summer (June to early August)	Breathable, quick-drying, and lightweight material (cotton voile, linen)	White, light blue, gray
Late summer to early autumn (end of August to September)	A texture that keeps you cool while allowing you to feel the changing seasons (tropical wool, lightweight cotton linen)	Navy, gray, beige, earth tones
Autumn (October-November)	A material with a moderate thickness and a refined appearance (wool flannel)	Brown, khaki, burgundy
Winter (December to February)	A material that offers both warmth and ease of layering (tweed, melton, and fleece blend).	Focus on dark tones, adding lightness with accessories.

Practical Guide: Outfit Mix-and-Match Techniques for Late Summer to Autumn - "Office Casual"
KUCHIMOTO'S [5 DAYS] 5 STYLES

A 1-week outfit plan for the late summer to early autumn season.

day of week	[Late Summer to Autumn Outfit Ideas]	Scene point
Monday	① Navy jacket + ② White shirt + ⑤ Navy pants + ⑧ Brown loafers	★A stressful start to the week. A day filled with meetings. In the setup, select "Enable ON mode".
Tuesday	③ Light blue polo shirt + ⑥ Gray slacks + ⑧ Brown loafers	A workday primarily focused on in-house activities. Combining freshness and elegance
Wednesday	① Navy jacket + ④ Gray knit + ⑦ Beige chinos + ⑨ White sneakers	Days involving frequent travel (going out) and business meetings. A jacket, chinos, and sneakers create a sophisticated look.
Thursday	② White shirt (sleeves rolled up) + ⑥ Gray slacks + ⑨ White sneakers	★High level of relaxation. A day for focused desk work. Rolling up your shirt sleeves creates a relaxed look.
Friday	① Navy jacket + ③ Light blue polo shirt + ⑦ Beige chino pants + ⑧ Brown loafers	It exudes a weekend vibe without sacrificing sophistication. With a simple and basic color scheme

■Tips for mixing and matching outfits

The number of combinations increases by moving the jacket (①) and pants (⑤⑥⑦) separately. The key to smart outfit mixing and matching is to alternate between "days when you wear the set together" and "days when you wear the pieces separately."

PICKUP COORDINATE
[Monday]

■Even if you have a sudden business meeting with a client, you'll be fine! "Office casual" outfits that work in a wide range of situations.

• ① Navy jacket, ⑤ Navy pants (set)
  ② White Oxford button-down shirt ⑧ Brown suede loafers

In the business world, there are always situations where you might receive an unexpected call saying, "A client will be visiting this afternoon." Whether you can handle such a situation calmly depends on whether you have the right items for high-pressure situations.

Why is a setup recommended?
A matching set is "not a suit, but it has a similar level of sophistication." The coordinated top and bottom create a sense of unity, making it easier to make a good first impression on someone you're meeting for the first time. Furthermore, since the jacket can be removed, it functions as casual attire within the company, allowing you to switch between work and leisure throughout the day.

PICKUP COORDINATE
[Thursday]

• ■On days when you need to concentrate on desk work, relax and wear a white shirt to stay focused.

• ② White Oxford button-down shirt ⑥ Gray slacks ⑨ White leather sneakers

This style features a button-down shirt for a relaxed yet polished look, with a neat collar. For bottoms, choose a material that is comfortable even when sitting for long periods and is wrinkle-resistant. Pair it with sneakers for a relaxed style that helps you maintain focus.

Tips for effectively using men's clothing and your existing wardrobe

Benefits of consulting at Isetan: Fitting, brand and size recommendations

I often hear people say, "Why not just buy it online yourself?" While it's true that information is readily available these days, there's something irreplaceable about the experience of "actually trying things on and getting advice from a professional" when it comes to office casual wear.

① The difference in fitting is obvious.
For office casual wear, "fit" is crucial, so we highly recommend trying on clothes. The fit of a jacket, in particular, is determined by the balance of shoulder width, chest circumference, and sleeve length. Isetan attendants offer fitting suggestions tailored to your body type and can also guide you through alterations as needed.

② Isetan Shinjuku Men's Building offers cross-brand comparisons , bringing together numerous domestic and international brands. Because you can compare multiple brands based on your budget, preferences, and intended use, it's an environment where you can easily find something that truly suits you without any preconceived notions of "I like this brand."

③ You can receive advice from the perspective of the overall coordination.
Men's attendants are professionals who can look at your entire outfit and offer advice .
We have staff members who hold qualifications in personal color analysis and body shape analysis®, and we excel at making suggestions that bring out the best in our clients.

Frequently Asked Questions (Solutions to problems categorized by age and season)

Q1. Are polo shirts really acceptable as office casual attire?
A. It's OK depending on the material and color.
While sporty polo shirts made of pique fabric tend to have a strong casual feel, polo shirts made of smooth fabric or high-density cotton can easily be worn as office casual wear by choosing basic colors such as navy, gray, or white. Pairing them with slacks or chinos and choosing loafers will further enhance their sophistication.

Q2. Can denim be worn as office casual attire?
A. It depends on the workplace culture, but if you choose it correctly, it can be used.
The three key requirements are: "dark indigo or black," "tapered silhouette," and "no damage or fading." Pairing them with a jacket further enhances their sophistication, making them suitable for office casual wear in many workplaces. If you're unsure, we recommend starting with dark indigo.

Q3. What kind of items should I invest in once I turn 40?
A. In order of priority, the items are: "jacket (or suit)", "leather shoes", and "belt".
These three points are the "visible parts and the parts that determine elegance," and simply choosing items with high quality materials can significantly change the overall impression of your outfit. While you can maintain a clean look even with relatively inexpensive tops and innerwear, we strongly recommend paying attention to the material and fit of your jacket and shoes.

Q4. For late summer (end of August to September), what specific items should I switch to autumn-appropriate office casual wear?
A. The basic principle is to "use autumn colors first, then gradually incorporate autumn materials."
Wearing thick materials while temperatures are still high will cause you to sweat and detract from a clean appearance. Start by switching to camel, brown, and khaki colors. For material changes, gradually incorporating lighter wool and polyester blends from cotton and linen blends from late September to October will allow for a smooth transition.

Q5. I want to incorporate sneakers into my office casual wardrobe, but what kind should I choose?
A. Simple leather sneakers are a safe choice.
White leather sneakers, in particular, exude a clean and sophisticated look and pair perfectly with jackets, slacks, and chinos. Suede sneakers are also recommended as they add texture to autumn outfits. What you should avoid are platform running shoes and athletic sneakers from sports brands. No matter how casual your workplace is, these tend to look too sporty and stand out in a negative way.

Q6. Is there anything I need to prepare when I go to the men's department for a consultation?
A. No special preparation is needed. However, if you have a rough idea of "how you want to change your current wardrobe" and "what kind of workplace and situations you want to use the clothes for," the male attendants will be able to make more specific suggestions.
Furthermore, if you come to our store wearing shoes and watches that you usually wear, we can offer more precise suggestions from a total coordination perspective. Many customers come to us not knowing where to start, so please rest assured that we will carefully guide you from there.


The key to successful office casual attire is knowing "how to choose the right clothes" and "how to wear them correctly." This involves mastering the basics of balanced size, material, and color, dressing appropriately for the season, and having items suitable for different occasions on hand. Simply following these three points will elevate your business attire to the next level, regardless of your age, including your 30s and 40s. If you're unsure, consult the men's attendants at Isetan Shinjuku Men's Building. They'll help you find the perfect office casual look tailored to you.

Book your appointment with a male attendant here | Isetan Men's Meet Ism

Our dedicated men's stylists, who hold professional qualifications in areas such as personal color analysis and body shape analysis®, will propose a "suitable styling" that enhances your charm based on your diagnostic results. ▶ Learn more here

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