The story
Chūgen Railway began to operate the railway line between Koizumimachi (currently Oizumi) and Tatebayashi on March 12, 1917. It changed its name to Jōshū Railway (上州鉄道, Jōshū Tetsudō) in 1922, and it was purchased by Tobu Railway in 1937. Since then Tobu Railway has operated the line as the Koizumi Line.
From Wikipedia’s article on Chūgen Railway, shared under CC BY-SA 4.0.4