A curved leaf spring which is a first urging member surrounds an outer wheel of a second bearing, and urges, through the second bearing, a second end of a worm shaft in a direction in which the distance between the center of the worm shaft and the center of a worm wheel is shortened. A second urging member includes an annular support member received by an end surface of the outer wheel and a plurality of elastic pins extending in a direction in parallel with the axial direction of a support member. The elastic pins have fixed ends fixed to the support member and free ends that come into elastic contact with an end wall of a housing.