was a Japanese politician, a member of the National Diet and a Cabinet member.
Koyama was born in Kobayashi, Miyazaki. He graduated from Kagoshima Prefectural Daini-Kagoshima Middle School (now Kagoshima Prefectural Konan High School) in 1923 and from Third Higher School (now Kyoto University) in 1926.
In 1929, he graduated from Faculty of Law, Tokyo Imperial University (now University of Tokyo) and joined Mitsubishi Bank. Later, he served as the committee chairs of Mitsubishi Bank Employees' Union.
Koyama was first elected to a member of the House of Representatives in 1949 and was elected 12 times. He served as Minister of Construction in the Cabinets of Hayato Ikeda and Eisaku Satà Â, and Director General of Environment Agency in the Cabinet of Kakuei Tanaka. In the National Diet, he served as the chief of the Judge Impeachment Court, the Chairs of Committee on Agriculture, Forestry and Fisheries of the House of Representatives, and the Chairs of Committee on Budget of the House of Representatives. He received the Grand Cordons of the Order of the Rising Sun in 1976.