Born in Kure, Hiroshima, Kōyama joined the Bungakuza theatre troupe in 1952, first as a directorial assistant and then as an actor.

[1] He made his film debut in 1953 in Tadashi Imai's An Inlet of Muddy Water.

[1] He left Bungakuza in 1963 and participated in other troupes such as Gekidan Kumo and Engeki Shūdan En.

[1][2] He was also well known for his role in the hit TV show The Guardman.

[1][2] He died in Kyoto Prefecture from pneumonia on 3 January 2017, 13 days before his 88th birthday.