From April 1964 onwards he lectured at the newly founded Dokkyo University on a full-time basis until his retirement in March 2005 to become an emeritus professor. A representative of Showa History Research Institute, he frequently joined controversies surrounding Japan's wartime past, particularly the denialism or minimization of the Nanking Massacre of 1937–38.
He began lecturing at Dokkyo University full-time starting April 1964 and continued until his retirement in March 2005. He was a representative of Showa History Research Institute, frequently engaging in discussions about Japan's wartime history, especially regarding the Nanking Massacre from 1937 to 1938.