In an actuator (1) in which an angle detector (13) of a magnetic encoder for detecting the rotational position of a motor (3) is incorporated inside a wave reduction gear (5), detection signals from Hall elements (11a, 11b) of the angle detector (13) are transmitted via sensor lead wires (17) that have been brought out through wiring holes (36a, 33a, 35a, 37a) formed inside the motor (3) to a sensor signal converter board (14) disposed on the rear end side of the motor. Since the wiring is not required to be brought out to the exterior, indirectly routed along the exterior of the motor (3), and brought out to the rear side thereof, the wiring is not mechanically damaged and can be brought out with the shortest possible wiring distance, and the effect of electromagnetic noise can be reduced.