You have probably already meet japanese salary-men and women, quite strictly dressed in the street. In fact, in Japan, when you meet clients, you usually need to wear a jacket, a shirt with long sleeves and a tie for mens. This is considered as impolite to do not be suitably dressed.
However, this strict dress code change a little bit through the year.
You may have heard of the “Cool biz” or “super cool biz” campaign in Japan.
What is it ?
The campaign has been introduced by the Environment Ministry in 2005 with the aim of reducing CO2 emissions and electricity use. The campaign promotes energy conservation in the workplace by urging people to dress lightly and casually and set their thermostats at 28 degrees (or about 82 °F) from June to September.
At first this campaign was for the Japanese government staff, but then it spreads to the private sector.
After 2011, to cope with power shortages triggered by the Fukushima nuclear crisis, the period of the campaign lengthened from May to October, it didn’t changed since, and the campaign was called “Super Cool Biz”.
Of course it depends of companies, but usually if your company participates to this "Cool Biz" campaign, you are allow come to the office without bringing a jacket. In the facts, many employees keep a jacket in the office for the emergency case, if they need to meet a big client. But mainly, they don't wear it all the day.
Once the Cool Biz period is over, everyone will come back to the usual dress code, and ties will do their coming back.