Abstract: Worm wheel construction that is able to sufficiently increase the strength of the connecting portion between a hub 11a and a gear portion 12a, and to maintain sufficient durability even when applied to an electric power steering apparatus that applies a large auxiliary torque, is achieved. A synthetic resin gear portion 12a is molded and formed in the end portion on the outer-diameter side of a metal hub 11a. A first annular concave portion 15 is provided on one surface side in the axial direction of the hub 11a, and a second annular concave portion 22 is provided on the other surface side in the axial direction thereof. Part of the synthetic resin of the gear portion 12a is fed into the portions near the outer diameter of the first annular concave portion 15 and the second annular concave portion 22 to form a first restraining portion 18 and a second restraining portion 23.

Abstract: A power assist apparatus includes an electric motor, a speed reducer, an annular torque sensor, a housing in which the speed reducer and the torque sensor are arranged, and an annular center aligning bracket. The housing includes a first housing element and a second housing element, and one of the first housing element and the second housing element is made of a synthetic resin. The center aligning bracket is fixed to the one of the first housing element and the second housing element by insert molding such that the center aligning bracket is concentric to the one of the first housing element and the second housing element. The first housing element and the second housing element are joined such that the first housing element and the second housing element are engaged with each other in an axial direction of the torque sensor via the center aligning bracket.