The vehicle seat includes a collision sensor provided to a seat back frame and being movable relatively backward by a rear-end collision, a headrest attached to the seat back frame and being movable between a normal support position and a head protection position anterior to the normal support position. The headrest is movable from the normal support position to the head protection position when the collision sensor is moved backward. The vehicle seat has a lock mechanism attached to the seat back frame. The lock mechanism is moved to a lock position by inertia when receiving an external force by a rear-end collision to regulate a return of the headrest from the head protection position to the normal support position.