To provide an electric power steering apparatus excellent in an operation feeling, in which an oil film formation property of grease on a tooth surface of each tooth of a worm wheel made of a resin composition including reinforced fibers is improved, a continuous oil film can be formed between the tooth surface and a tooth surface of a worm, a frictional coefficient of sliding between both the tooth surfaces is effectively reduced by lubrication by the oil film and operation torque is reduced as much as possible.

A surface roughness R_a of a tooth surface 25 of each tooth 21 of a worm wheel is set within a range of 0.1-0.5 μm, especially within a range of 0.3 μm or less. The worm wheel is manufactured by forming a resin member 22 to be a base of the tooth 21 from a resin composition including reinforced fibers, forming the tooth 21 by toothed wheel cutting, and then performing fitting processing of the tooth 21 to adjust the surface roughness R_a of the tooth surface 25.