He graduated from Law Department, Tokyo University in 1898. He went to Belgium to study the savings system.
After graduation Kainan Shimomura was appointed official of the Communications Ministry. Later became director of the Ministry's Savings Bureau. He was Civil Governor of Formosa and director general of the General Affairs Bureau, Government-General of Formosa (1915-1921).
After a year's travel in Europe and the United States, he was appointed vice-president of the Asahi Shimbun, which post he held for 10 years. He retired in 1936 and became president of the Japan Broadcasting Corporation.
Toward the end of World War II, he was State Minister and director of the Information Bureau in the cabinet of Admiral Kantaro Suzuki. He was a lecturer on public finance at Waseda, Hosei and Chuo universities and Tokyo University of Commerce. He a accorded his doctorate (1919).