專賣局
Hamaguchi was born in Nagaoka District, Tosa Province (now part of Kōchi city, Kōchi Prefecture on the island of Shikoku). He was the third son of Minaguchi Tanehira, an official in the local forestry department, and took the Hamaguchi name on his marriage to Hamaguchi Natsuko in 1889. Hamaguchi graduated from the Law College of Tokyo Imperial University in 1895 and began his career as a bureaucrat in the Ministry of Finance. In 1907, he rose to the position of Director of the Monopoly Bureau. He became Vice Communications Minister in 1912 and Vice Finance Minister in 1914.