Yamagata Kikai Kōgyō K.K. (山形機械工業㈱) was a Japanese company founded in December 1946. It was dependent of Tōkyō Kōgaku and was based in the town of Yamagata (山形). It made the Semi Oscon 4.5×6 folder, distributed by Ōsawa Shōkai in 1953 and 1954, with lenses provided by Tōkyō Kōgaku. It became K.K. Topcon Yamagata (㈱トプコン山形) in 1971 and still (2007) exists under that name.
- See the chronology of the Topcon official website and the chronology of the Topcon Yamagata official website. Lewis, p.79, says that it was affiliated with Nippon Kōgaku, certainly by mistake, whereas Sugiyama, item 1381, says that it was a supplier of Nippon Kōgaku.
- See the chronology of the Topcon Yamagata official website. Lewis, p.79, says that it "went out of business", certainly by mistake too.
- Lewis, Gordon, ed. The History of the Japanese Camera. Rochester, N.Y.: George Eastman House, International Museum of Photography & Film, 1991. ISBN 0-935398-17-1 (paper), ISBN 0-935398-16-3 (hard). P.79.
- Sugiyama, Kōichi (杉山浩一); Naoi, Hiroaki (直井浩明); Bullock, John R. The Collector's Guide to Japanese Cameras. 国産カメラ図鑑 (Kokusan kamera zukan). Tokyo: Asahi Sonorama, 1985. ISBN 4-257-03187-5. Item 1381.