He attended the 3rd class of the Imperial Japanese Army Academy and was commissioned as a second lieutenant in the cavalry in 1893.

He was promoted to major general in July 1918 and made commandant of the Cavalry School.

He was assigned command of the newly-formed IJA 14th Division in March 1926 and entered the reserves shortly thereafter.

Ōshima was chosen to head the Japanese equestrian team at the 1932 Summer Olympics in Los Angeles.

One of his team members, Takeichi Nishi won the gold medal at this event for show jumping.