A backrest frame 5 is provided with a cushion plate 31 of one substantially square plate form positioned behind the waist from the upper part of the back of a vehicle seat occupant, movably back and forth by way of a plurality of upper and lower parallel seat springs, one end of either one of a pair of right and left seat springs 34B of the plurality of upper and lower parallel seat springs is connected to a pair of lower link mechanisms 35 provided rotatably on the backrest frame 5, and a rear end collision sensor 40 is formed by the cushion plate 31 between the seat springs 34B for moving a headrest 4 forward, and a coupling part 39 of the other end of the seat spring 34B is directly attached to the lower link mechanism 35.