According to the theory that he was born in Mikawa, he was a younger brother of 長田重元 (Shigemoto OSADA), a descendent of 長田親政 (Chikamasa OSADA), who defeated Yoshitomo MINAMOTO.
三河出生説に拠れば、源義朝を討ちとった長田親政の子孫である長田重元の弟とされる。