An electric power steering apparatus including a reduction mechanism 5 for transmitting an output of a steering assist motor 1 to a steering mechanism through a worm 3 and a worm wheel 4, in which the worm wheel 4 is formed by a thermosetting synthetic resin filled with a sheet 6 of aramid fibers having a low attacking property to a counter member and an effect of improving the abrasion resistance of the synthetic resin. Even when the reduction mechanism is used in an engine room or the temperature of the reduction mechanism is raised by frictional heat with heightening power, the reduction mechanism is durable, and further the gears have excellent abrasion resistance and toughness and improved durability.