Masatarō Shimizu (清水 正二郎, Shimizu Masatarō; 26 April 1925 – 23 May 1994), known by his pen name Koshi Kurumizawa (胡桃沢 耕史, Kurumizawa Kōshi), was a Japanese writer of detective fiction during the Shōwa era.
Source: “Koshi Kurumizawa”, English Wikipedia (CC BY-SA 4.0), excerpt