A pair of seat backs are arranged in a vehicle width direction. A pair of floor brackets attach outer end portions of the seat backs in the vehicle width direction to a floor of the vehicle. A pair of center hinge brackets attach inner end portions of the seat backs in the vehicle width direction to the floor. A supporting bar is separated from the floor, is extended in the vehicle width direction and is disposed behind the seat backs. The seat backs are independently pivotably attached to the floor. Both end portions of the supporting bar in the vehicle width direction are attached to the floor brackets. A center portion of the supporting bar in the vehicle width direction is attached to the center hinge brackets.