Last year's (2015) sales of department stores in Japan were 6.1 trillion yen. Nikkei newspaper estimated that Mitsukoshi-Isetan was the biggest chain, having 19.3% of the market share.
Figure: Department Store Market Share in Japan, 2015
|Store||Market share (%)|
Source is Nikkei Sangyo Shimbun newspaper, the article on 2016 July 25th.