A head rest apparatus comprises a sole stay, a head rest main body movably supported on the sole stay, a guide rod fixed in the head rest main body, a rail disposed in the head rest main body and fixed on the sole stay, a guide member slidably supported on the guide rod and the rail, a screw rotatably supported in the head rest main body, a nut supported on the rail and engaged with the screw, a cushion disposed between the rail and the nut, and a motor connected to the screw or the nut. A load imparted to the head rest main body is absorbed by the sliding movement of the guide member and the distortion of the cushion.