This paper describes five reasons that Japanese retailer`s investment in Southeast Asia. 1) Aging Society in Japan and downsizing Japanese markets, 2) They expect to grow the middle class in Southeast Asia, 3) the development of supply chain, 4) Diversifies strategy rather than the concentration in China market, 5) Increasing inbound tourists to Japan will strengthen Japanese retailers and product brand equity. This paper also mentions the case of Japanese department stores and convenience stores in Southeast Asia. 7-Eleven has the highest share of among Japanese convenience stores. The fact that the number of Japanese convenience stores is declining in Europe and the US is expected to compete with local Asian companies even in Southeast Asia in the near future.