A rotary actuator includes a multi-polar magnet, in which north and south poles are alternately arranged in a circumferential direction, the multi-polar magnet being shaped into one of a circular ring and a circular arc member; and a coil body having coils which are provided around the multi-polar magnet to be capable of moving in the circumferential direction of the multi-polar magnet, each of the coils substantially lying on a plane that extends in a radial direction of the multi-polar magnet and orthogonal to the circumferential direction of the multi-polar magnet. The north and south poles of the multi-polar magnet are positioned apart from each other by a predetermined interval in the circumferential direction. Dimensions of each coil are predetermined so that length of each coil in the circumferential direction is associated with the predetermined interval. Predetermined currents are passed through the coils in a properly phased manner.