Kintaro Oba became managing director of the newly established Hakone Yuransen Kaisha (Excursion Ship Company) (1920). When that company was merged into Sunto Railway Company became its senior managing director.
Appointed auditor of Kokudo Keikaku Kogyo Kaisha (National Land Planning Industrial Company) (1943) and senior managing director of Gakunan Railway Company (1948). Holds various additional posts including those of councilor of National Park Council, director of Odawara and Mishima Chambers of Commerce & Industry and member of Numazu Rotary Club.