For Business: a Full Suit in Japan
Always Were Formal Attire in Japan During Business Related Events
Pretty much every businessman in Japan wears a full suit to work everyday. This is what allows the domestic suit company Aoyama to boast that it sells the most number of suits among all suit companies around the world. In Japanese business, not only are results considered important, but also attitude towards work. Unlike in the West where people tend to base your business value in the results you realize, the means with which you realize your results and your attitude are regarded highly in Japan. Wearing a full suit is one way to show a positive and dedicated attitude towards work.
It is only during the summer, and only in recent years, that employees are allowed to leave their ties at home and wear short sleeve dress shirts. This is the "cool-biz" (cool business style) that is common these days. Still, on a business occasion, it is wise to always air on the conservative side to avoid giving off a bad impression.