In 1915 he graduated from the political and economic course of Waseda University and for a time worked as a reporter for the Hochi Shimbun and Tokyo Nichinichi Shimbun.
In 1927 he became a member of the staff of the magazine Rodo, helping to formulate the system of thought associated with the so-called Labor-Farmer faction within the socialist movement.
In 1928, after the government had ordered the dissolution of the Rodo Nominto, he became chief secretary of the Musan Taishuto (Proletarian Popular Party). When the latter party split apart, he became a member of the standing committee of the Nihon Taishuto (Japan Popular Party). In 1930 he became a member of the central executive committee of the Zenkokii Taishuto (National Popular Party) and also served as chief secretary of the Nihon Musanto (Japan Proletarian Party) and director of the Nihon Keizai Kenkyukai (Japan Economic Study Society), working in the early thirties to combat the growing trend toward fascism in Japan. In 1937 he was arrested along with a number of other left-wing leaders when the government carried out the first of its so-called jimmin sensen (popular front) actions. His appeal was pending when the Pacific War came to an end.
In 1947, when the left wing cooperated with the more conservative forces to bring about the formation of a socialist cabinet headed by Katayama Tetsu, he joined with the labor unions in opposing the government. In 1949 he became chief secretary of the Socialist Party and, in 1951, after the party had split, he became chairman of the Saha Shakaito (Leftist Socialist Party). He resigned this post in 1960 but continued to be an advisor to the party. During the period preceding his resignation he was active on the international scene as well, in 1951 attending the Socialist Internationale in Berlin, East Germany, and later becoming a secretary of the organization. In 1952 he proposed the holding of a congress of Asian socialist parties, traveling to many countries in Asia to implement the plan and later becoming honorary president of the congress. During the period from 1946 to 1966, he was elected nine times as a member of the Lower House of the Diet. He compiled a collection of materials dealing with social problems and the socialist movement that was made public under the title Shakai bunko.
He traveled about America, Europe, and the Soviet Union and on his return to Japan devoted his energies to the study and encouragement of socialism, founding an organization known as the Seiji Kenkyukai (Political Study Society) toward the close of the Taisho era. He took part in the socialist movement to the extent that such activities were permitted by the laws of the time, helping to found the Nomin Rodoto (Farmer Labor Party) in 1925 and the Rodo Nominto (Labor Farmer Party) in 1926.
In the postwar period he was active in the Nihon Shakaito (Japan Socialist Party) from the time of its founding, being associated with the left-wing faction of the party.