Imanishi was born in Hiroshima on January 12, 1941. After graduating from Tokyo University of Education, he joined his local club Toyo Industries (later Mazda) in 1963. In 1965, Toyo Industries joined new league Japan Soccer League. The club won the champions for 4 years in a row (1965-1968). The club also won 1965, 1967 and 1969 Emperor's Cup. He retired in 1969. He played 42 games in the league. He was selected Best Eleven in 1966.
After retirement, Imanishi became a manager for Mazda as Teruo Nimura successor in 1984. This season was the first season the club was relegated to Division 2. He promoted the club to Division 1 in 1986. In 1987, he resigned a manager and Hans Ooft became a new manager. However, the club was relegated to Division 2 again in 1988. Imanishi became a manager as successor Ooft again in 1988. Imanishi promoted the club to Division 1 in 1991 and he resigned in 1992. From 1994, he worked for Japan Football Association until 2002. He also served as president at FC Gifu from 2008 to 2012.