A first concave-convex part is formed in an outer diameter side circumferential surface of a first annular concave part provided in an axial one-side surface of an inner wheel element, and a second concave-convex part is formed in a bottom surface of a second annular concave part provided in the axial other-side surface of the inner wheel element. An outer circumferential part of the inner wheel element is embedded in an outer wheel element, and synthetic resin forming the outer wheel element partially enters into a plurality of concave parts constituting the first concave-convex part and the second concave-convex part. Thus, a configuration is achieved in which the holding power of a synthetic resin outer wheel can be secured from the metal inner wheel element, and the manufacturing error can be suppressed in the worm wheel tooth part provided in the outer circumferential surface of the outer wheel.