[Object] To detect a rotational angle accurately and also to drive more safely. [Solution] Provided is an actuator (300) including: a reduction gear (320) that reduces, by a certain reduction ratio, a rotational velocity of an input shaft joined to a rotary shaft of a motor (360), and transmits the reduced rotational velocity to an output shaft (350); a first absolute angle encoder (330) that detects a rotational angle of the input shaft; and a second absolute angle encoder (340) that detects a rotational angle of the output shaft.