[1] He attended the private Kawabata Art Academy (川端画学校, Kawabata Gagakkō) in Koishikawa (now part of Bunkyō, Tokyo), after which he began attending Taiheiyō Fine Arts Academy before dropping out partway through school.
From his elementary years through high school, Kojima began drawing manga, and in 1949 he made his professional debut as a member of the Dokuritsu Mangaha.
That group broke up in 1959, and in 1964 he joined the Japan Manga Artist Cooperative and the Manga Shūdan, participating in both groups regularly.
Other works include the long running Sennin Buraku, as well as Hige to Boin, which ran from 1974 to 2014 in Shogakukan's Big Comic Original manga magazine.
Kojima made regular appearances on the Tokyo 12ch (now TV Tokyo) news discussion show Asahi Shimbun Wide News where he discussed current events and shared satirical illustrations with the viewers.