Vehicular seat including forward movable headrest

A vehicular seat (1) includes at an upper part of a seat back (3) an upper frame (6) which extends in a widthwise direction of the seat back (3). An actuator unit (16) which generates a drive force is attached along the upper frame (6). A headrest support frame (8) is provided to the upper frame (6) so as to be capable of moving in a front-and-back direction. When an acceleration equal to or above a predetermined value is applied to a vehicle by a collision from behind, a drive force generated by an operation of the actuator unit (16) is transmitted to the headrest support frame (8). By moving the headrest support frame (8) in a direction along which it approaches an occupant (M) by using this drive force, a headrest (9) supported to the headrest support frame (8) moves frontward.