When a pressure receiving plate provided at a seat back moves to a rear side of a vehicle body when a vehicle is collided from behind, a Bowden cable transmits movement of the pressure receiving plate to a headrest ascending mechanism as a tensile load, thereby quickly ascending a headrest to reliably hold a head of an occupant. The Bowden cable transmits only the tensile load, and hence the Bowden cable is not buckled. Reduction in weight is made possible as compared with the case using a rod for transmitting a compression load. Since the Bowden cable is light, it is not required to unreasonably place the pressure receiving plate at a position near the headrest ascending mechanism for reduction in weight, and hence the pressure receiving plate can be placed at the optimal position where a sufficient driving force is obtained at the time of collision. Thus, a headrest is ascended with favorable responsiveness upon a rear-end collision of a vehicle while using a thin transmission member with low rigidity.