Koichi Takemasa (武正 公一, Takemasa Kōichi, born March 23, 1961) is a Japanese politician serving in the House of Representatives in the Diet (national legislature) as a member of the Democratic Party of Japan. A native of Shimizu, Shizuoka and graduate of Keio University he was elected for the first time in 1995 after an unsuccessful run in 1991.