Iwashita was born in Shizuoka Prefecture on April 8, 1973. After graduating from high school, he joined new club Shimizu S-Pulse based in his local in 1992. He got a opportunity to play little by little from first season and the club won the 2nd place 1992 and 1993 J.League Cup. Although he played many matches as forward in 1994, his opportunity to play decreased in 1995. In 1996, he moved to Japan Football League club Vissel Kobe. However he could hardly play in the match. In 1999, he moved to Japan Football League club Jatco (later Jatco TT). He played many matches as regular player and retired end of 2001 season.