Amemiya Keijiro was born on October 24, 1846, in the village of Ushioku,[2] Kai Province, into the family of a feudal lord.

He moved to Yokohama in the early 1870s and tried to work in the market for raw silk, Western silver, and silkworms.

After that, he decided to invest in the fields of social infrastructure, which were profitable in the western countries, such as railroads, iron manufacturing, and water supply.

[5] The land he cultivated at that time still remains today as "Amamiya Shinden" in Nagakura, Karuizawa-cho, Kitasaku-gun, Nagano Prefecture.

[5] In 1888, he made a large profit by speculating in the Koumu Railway, which connected Shinjuku and Hachioji and was the predecessor of the Chuo Main Line, and when the stock price slumped due to internal company conflicts, he bought it up and became a director of the company.