Kei Kumai, who has died aged 76, was a distinguished Japanese film-maker whose work combined dramatic force with trenchant social criticism. He worked with many of Japan's most famous actors, and filmed a script left unrealised by world-renowned colleague Akira Kurosawa (obituary, September 7 1998). Yet he was neglected abroad, perhaps because he eschewed the fashionable experimentation of such New Wave contemporaries as Nagisa Oshima. Instead, he adopted a style of powerful simplicity, charting controversial themes with rare directness.

Born in the village of Azumino in mountainous Nagano prefecture, Kumai became interested in cinema while a student at Shinshu University. Upon graduation in 1953, he entered the industry as an assistant director. A decade-long apprenticeship at Nikkatsu studios preceded his directorial debut, The Long Death (1964), a thriller based on a notorious 1948 mass poisoning. Japanese Archipelago (1965), another thriller, dealt with the murder of an American serviceman. Both films used murder investigations to examine the legacy of Japan's wartime aggression and defeat; the latter also subtly criticised American foreign policy in Asia....

The early 1970s were his richest period. This Swarming Earth (1970) detailed the discrimination suffered by Koreans, atom bomb survivors and the burakumin under-class. His best-known film, Sandakan 8 (1974), examined the taboo subject of Japanese women sold into prostitution in south-east Asia early in the 20th century. The great actor Kinuyo Tanaka gave a poignant performance as a former prostitute ostracised because of her past.