BACK FRAME

A back frame, which forms a framework of a seatback, includes a back side frame, a stopper, and an extending portion. The back side frame is rotatable with respect to a cushion frame in seat front-rear directions. The stopper is fixed to the back side frame and includes a contact portion. When the contact portion contacts a contact target portion that is immobile with respect to the cushion frame, the stopper restricts rotation of the back side frame. The extending portion extends from the stopper in the seat front-rear directions. The extending portion is fixed to the back side frame in at least a part of the extending portion.