Hailing from
Nagano Prefecture, Kosaka was born into a politician family on 23 January 1912. His grandfather, Zennosuke Kosaka, was the founder of the daily
Shinano Mainichi and a politician. His father, Junzo Kosaka, was also a politician. His younger brother, Tokusaburo Kosaka, was a leading politician of the
Liberal Democratic Party. Zentaro Kosaka was a graduate of Tokyo University of Commerce (present-day
Hitotsubashi University). ==Career==