To increase rigidity and suppress occurrence of vibration and noise caused by vibration without increasing weight.

A worm wheel of a worm reduction gear is composed of a metallic core unit 10 fixed to an output shaft and a gear part 20 made of synthetic resin, fixed to an outer peripheral part of the core unit 10, and having a gear tooth face. The core unit 10 is composed of a boss part 11 and a rim part 12 and is molded by, for example, cold forging. A radial rib 13 extending toward the outer periphery from the boss part 11 is provided in the rim part 12 of the core unit 10. This rib 13 is molded in a cold forging process for molding the core unit 10. As a result, rigidity of the core unit 10 can be increased and vibration and noise can be suppressed without increasing weight.

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