From Wikipedia:

Publisher of mystery fiction, science fiction, fantasy, literary fiction and social science, based in Tokyo. It began as the Tokyo branch of a publisher called Sōgensha of Osaka in 1925 and spun-off in 1948.

Its imprint, Sōgen Suiri Bunko, started in 1959, is one of the leading Bunkobon labels focusing on mystery, science fiction, fantasy, and horror.