An output portion is formed integrally with an output gear made of a magnetic material and is rotated integrally with the output gear. A yoke is placed at the output gear and includes first and second yokes. An arcuate gap, which extends along an arc that is centered at a rotational center of the output gear, is formed between the first yoke and the second yoke. A magnet is installed between one end of the first yoke and one end of the second yoke. Another magnet is installed between another end of the first yoke and another end of the second yoke. A Hall IC is placed in the arcuate gap and is movable relative to the yoke. Primary holes are formed between the rotational center and the yoke such that the primary holes extend through the output gear in a plate thickness direction of the output gear.