A sectoral reduction gear is arranged between a motor portion and a link mechanism. The sectoral reduction gear rotates in a reciprocating manner in a predetermined angle range on the basis of a forward rotation and a reverse rotation of the motor portion. An outer periphery of the sectoral reduction gear defines an imaginary circle. An inner region of the imaginary circle has an operating range in which the sectoral reduction gear, which rotates in a reciprocating manner, passes, and a non-operating range, in which the sectoral reduction gear does not pass. As seen from an axial direction of an output shaft, a part or the whole of the output shaft is arranged in the non-operating range.