When a vehicle is rear-ended and a seated user moves rearward in reaction to the rear-end collision, a load generated by a rearward movement of a lumbar portion of the seated user is transmitted from a pressure plate of operating force generating means to an operating force generating mechanism. Then, a pressure roller of the operating force generating mechanism deflects and pulls inner cables of pulling cable devices, thereby moving both end portions of a headrest frame upward. As a result, the headrest frame is moved upward along with headrest supporting brackets smoothly and reliably, whereby a headrest attached to the headrest supporting brackets with headrest stays arranged between the headrest and the respective headrest supporting brackets is moved in the upward-forward direction, that is, toward the head of the seated user smoothly and reliably.