There is provided an urging mechanism (B) that elastically urges a second end portion (23) of a worm shaft (20) that is supported so as to be pivotable about a first end portion (22). The urging mechanism (B) is configured to adjust a backlash between the worm shaft (20) and a worm wheel (21) by elastically urging the second end portion (23) in a perpendicular direction (Z1) that is perpendicular to a direction (Y1) in which an inter-axis distance (D1) between the worm shaft (20) and the worm wheel (21) increases and decreases, in a state where increases and decreases in the inter-axis distance (D1) is prevented.