PURPOSE: To ensure a fully reclining condition by automatically lowering a headrest device toward a seat back when the fully reclining condition is set.

CONSTITUTION: A manual switch MS1 is manipulated so as to drive an elevating drive motor 33 provided in a seat back in order to vertically move a headrest device. A manual switch MS2 is manipulated to drive a sliding drive motor 6 provided in a slide mechanism so as to shift a seat longitudinally of a vehicle. The seat back can be tilted into a fully reclining condition by means of a reclining mechanism, and when the seat back is tilted to an angle more than a set angle, a tilt angle detecting switch AS is turned so as to the elevating drive motor 33 is reversed to automatically store the headrest on the seat back side.