Lieutenant-General Masao Maruyama was a Japanese Infantry Officer, born in Nagano, Japan.
He was promoted to rank of Major-General on 15 July 1938 and to rank of Lieutenant-General on 1 March 1941.
Became commander of Japanese 6th Infantry Brigade on 15 July 1938 and a commander of 3rd Independent Defense Unit on 7 May 1940.
He assumed command of Japanese 2nd Infantry Division on 10 April 1941.
He participated in the campaign of the China Incident as a Commander of 6th Infantry Brigade and during the Pacific War, he took part in the campaigns of the Dutch East Indies and Guadalcanal as the commander of 2nd Infantry Division.
He was placed on reserve list on 2 March 1944.
He died on 11 November 1957.