After graduating from Hannan University, he joined the newly promoted J1 League club, Avispa Fukuoka in 1996.
In 2005, he did not play in any matches and he moved to the Japan Football League club Ehime FC in October.
[2] However in April, he was dismissed after only the ninth gameweek due to his team's poor performance, languishing in 20th place with 1 win, 4 losses and 4 draws.
[3] On 17 December 2021, Ishimaru returned to Ehime FC for the 2022 season, beginning his second stint in charge after managing them in 2013.
[4] On 11 November 2023, Ishimaru led Ehime FC to become J3 League champions, returning to the second tier for the 2024 season after a two year absence.