Kimura was born as Kinjiro Miyake (三宅 金治郎 Miyake Kinjirō) on 19 April 1897 in the fishing village of Kamiukawa. After he finished school at the age of 14, he worked for local post offices for over 45 years until he retired in 1962 at the age of 65. In the 1920s, he also worked as a government communications worker in Korea, which was at the time a colony of Japan.