Rigidity is improved at a part where side frame pieces overlap each other in a side frame. In a vehicle seat provided with a seat back frame, a side frame of the seat back frame has a first side frame piece and a second side frame piece partially overlapping each other in a direction of extension of the side frame. The side frame has an overlapping part where both the first side frame piece and the second side frame piece overlap each other. At the overlapping part, the side frame pieces overlap each other in a state where a plurality of closed regions and closed by being surrounded by both side frame pieces are formed in a cross section of the overlapping part intersecting with the direction of extension of the side frame.