<p>A headrest is attached to a square frame-shaped seatback frame so that the headrest can be moved back and forth by an upper lever. The upper lever is connected by a connection rod to a lower lever provided at the seatback frame. Left and right connection arms of a rear collision detector are attached to the lower lever.Backward movement of the rear collision detector moves forward the headrest via the connection rod and the upper lever. The connection arms of the rear collision detector are fixed to the lower lever, held at a predetermined angle.</p>
