PURPOSE: To increase the supporting strength of head rest without spoiling the operational merits by fixing the axial cylinder to both right and left sides of the head rest and detachably fitting pins in the fitting grooves of the axial cylinder.

CONSTITUTION: When the head portion 35 of a manipulating member 28 is pressed inwardly against the elastic force of a spring 36, the insertion part 29 at the front end of the manipulating member 28 and the deeper insertion part is transferred in the direction where the pins 33, 34 disengage from the fitting grooves 19, 25 of the axial cylinders 17, 28 fixing the detachable pins in the long holes 26, 27, and hence, the detachable pins 33, 34 are removed from the fitting grooves 19, 25. In this state, the head rest 4 is turned backward to adjust its position and the hand is made off the head portion 35 at a required position. So the manipulating member 28 returns to the original position due to the elastic force of spring 36 and, as a result, the detachable pins 33, 34 are fitted in the fitting grooves 19, 25 to turn the head rest 4 backward to a required position. By one pushing operation of the head portion 35 of the manipulating member 28, the head rest 4 can be turned backward to adjust the position even if it is in any place.