A base portion of a magnet holder attached to a rotor core of a rotor has a press-fit pin press-fitted into a press-fit hole provided at an end surface of the rotor core. An arm portion of the magnet holder has a holder rib which protrudes inward in the radial direction of an output shaft and of which one end surface in the circumferential direction serves as a pressing surface, and a come-off prevention protrusion inserted into an insertion groove provided at an outer circumferential surface of the rotor core. Magnets are located between the rotor core and the magnet holders, one end surface in the circumferential direction of each magnet contacts with the pressing surface, and another end surface contacts with a core rib protruding from the rotor core.