Keita Kamei Department of Economics, Seinan Gakuin University   Nishijin Sawara-ku, Fukuoka , Fukuoka 814-0002 日本   k-kamei@seinan-gu.ac.jp             JEL Areas: L1 : Market Structure, Firm Strategy, and Market Performance: General L4 : Antitrust Issues and Policies: General