It depends on what kind of industry you are in and what kind of job you do. If you belong to corporate staff working inside the office, business casual is a norm throughout the year. Shirts tend to be white and pants tend to be dark although more colorful combinations are seen nowadays. If your job is to meet customers, a suite and a tie are a must except for summer when you can usually wear just a shirt and pants. Established industries such as financial tend to have strict dress codes while those businesses like media and IT are less strict.
Outside business, there is a wide variety of styles for men in Japan; European (English, Italian classic) vs. American traditional, traditional vs. casual, mode, street. etc. Younger people tend to absorb different styles nicely to create unique Japan fashion. One distinct Japanese style can be seen among Otaku (a kind of nerd with passion into anime, character figures, computers, etc.) who are usually in a checkered shirt, out-of-date jeans, worn-out sneakers and a huge backpack!!