To prevent generation of impact noise of a high frequency generated in operation of a flapper.

The actuator 2 is provided with the flapper 30 turnably supported by a frame body 4, a tension coil spring 40 arranged between the flapper 30 and the frame body 4, a first stopper 22 positioning the flapper 30 in a first position, a second stopper 24 positioning the flapper 30 in a second position, and a driving means for turning the flapper 30 from the first position to the second position. The driving means comprises a wire 50 made of a shape memory alloy having one end and the other end mutually isolated and held by the frame body 4 and having an intermediate part connected to a part of the flapper 30.