A speed reduction unit (31) includes an input shaft (32) coupled to a motor rotary shaft (22) of a motor unit (21), an input gear (33) coupled to the input shaft, a cylindrical output shaft (41) coupled to an outer ring (12), and an output gear (40) coupled to the output shaft, and constructs a driving-force transmission path that reduces the rotational speed of the input gear and transmits the reduced rotational speed to the output gear. The output shaft is rotatably supported at both ends by a first output-shaft bearing (44) rotatably supporting an outer diameter of an axially outer end side of the output shaft and a second output-shaft bearing (46) rotatably supporting an inner diameter of an axially inner end side of the output shaft.