Born in Gifu Prefecture, Kōyama attended Nihon University but quit midway to join the independent production company Kindai Eiga Kyokai, where he worked as an assistant director under such directors as Kaneto Shindō, Kōzaburō Yoshimura, and Tadashi Imai. He made his directorial debut in 1971 with thechildren's film Koi no iru mura. His second film, Futatsu no hāmonika (1976), earned him a New Directors Citation from the Directors Guild of Japan. His 1983 film Hometown was entered into the 13th Moscow International Film Festival. His 1987 film, Hachiko Monogatari, about the faithful dog Hachikō, was the top Japanese film at the box office that year.He is known for his humanistic perspective.