Born in Toyohara, Karafuto (now Yuzhno-Sakhalinsk, Sakhalin), Fukushima was the son of a public official.
In 1954 he dropped out and began to study translation under Shunji Shimizu (清水俊二, Shimizu Shunji) and writing children's literature under Tatsuzo Nasu (那須辰造, Nasu Tatsuzō).
The following year, he initiated the Hayakawa SF series and in 1959 founded S-F Magazine and served as chief editor until he left the company in 1969.
He aimed to make SF more highbrow, and initially rejected space opera.
(see covers) He, along with Shinichi Sekizawa, wrote the 1974 film Godzilla vs. Mechagodzilla.