In 1204, when the Incident of Shigetada HATAKEYAMA occurred, Yoshitane supported Yoshitoki HOJO and defeated Shigetada even though he had a blood relationship with Shigetada (Yoshitane's grandmother was Shigetada's aunt).
1204年、畠山重忠事件が起こると、重忠と縁戚関係（義胤の祖母は重忠の叔母）であったにも関わらず、北条義時に与して重忠を討った。