He was the third director of the Riken Institute, a position which he assumed in 1921 and held for 25 years.

During this period, he was notable for establishing the Riken Konzern, a zaibatsu of companies which focused on utilizing Riken's research results to produce commercial products.

He married a daughter of his uncle Ōkōchi Nobuhisa, another son of Akikatsu but adopted by Matsudaira Nobuaki, with whom he had issue, including Nobuhiro Ōkōchi.

[1][2][3][4] Masatoshi was born in Hamamatsuchō, Minato, Tokyo as a descendant of the Ōkōchi-Matsudaira clan who ruled over the Ōtaki Domain.

After graduating from an elementary school affiliated with Gakushūin, he received an education at the First High School, and then enrolled in the Tokyo Imperial University.