the worm wheel 12 the first sliding surface 310 and the second sliding surface 320 face each other with a supporting shaft 121 between them when the worm wheel 12 turns the first sliding member 31 and the second sliding member 32 slide and come in contact with the protrusion 20 of the output lever 13 and guide the protrusion 20 to the guiding member 34 and the allowing member 35 respectively the contact member 33 is pinned on the worm wheel 12 by the supporting shaft 121 the contact member 33 includes a first contact member 331 and a second contact member 332 which extend in different directions with respect to the supporting shaft 121 when the worm wheel 12 turns clockwise the first contact member 331 attaches with the protrusion 20 of the output lever 13 and swings the output lever 13 counter clockwise the first contact member 331 is disposed in such a way that it does not attach with the protrusion 20 when due to the turning of the worm wheel 12 the protrusion 20 is moving along the second sliding surface 320 when the worm wheel 12 turns counter clockwise the second contact member 332 attaches with the protrusion 20 of the output lever 13 and swings the output lever 13 clockwise the second contact member 332 is disposed in such a way that it does not attach with the protrusion 20 when due to the turning of the worm wheel 12 the protrusion 20 is moving along the first sliding surface 310 the guiding member 34 is disposed between and in continuation.