He started playing football when he was in the 5th grade and was converted to a goalkeeper at high school. After graduating from Doshisha University in 1988, Kojima joined Fujita Industries F.C. (current Shonan Bellmare) playing in the Japan Soccer League division 1. He became a regular starting member of the team in 1994. He had been playing for the club as an employee of Fujita Industries but turned professional in January 1995.
His international debut came on June 6, 1995 against Brazil in the Umbro Cup. He was in the squad for the 1998 FIFA World Cup as the third GK but did not play any game in the tournament.