When a tilt-down function is performed, a rotationally-preventing condition of a reclining device connecting a base member and an intermediate member is released, so that a seat back is tiltably rotated forwardly integrally with the intermediate member and a seat cushion is pushed by a boomerang link capable of moving with the intermediate member so as to be sunk downwardly while tiltably rotating a front link. However, when a walk-in function is performed, a rotationally-preventing condition of a memory device connecting the seat back and the intermediate member is released, so that the seat back can be tiltably rotated to a forwardly inclined position independently of the intermediate member that is maintained in a condition in which the intermediate member is integrated with the base member.