Among the first to third wire covers 8a to 8c, the second wire cover 8b and the third wire cover 8c that lead out three lead wires are configured in a completely identical manner. Because the first wire cover 8a leads out six lead wires, a longitudinal dimension of a horizontal cross-section thereof is established so as to be less than a longitudinal dimension of a horizontal cross-section of the second wire cover 8b and the third wire cover 8c, which route only three lead wires; however, a basic configuration of the first wire cover 8a is similar to that of the second wire cover 8b and the third wire cover 8c. Therefore, a configuration of the wire covers used in the present embodiment is described below through an example of wire covers used as the second wire cover 8b and the third wire cover 8c.

A structure of the wire covers 8b, 8c used in the present embodiment is described in detail with reference to FIGS. 11 to 14. As shown in FIGS. 14(A) and 14(B), the wire covers 8b, 8c each integrally have a head part 801 arranged near one axial end of the wire leading-out hole (i.e., on an end side of the wire leading-out hole that opens toward the exterior) when the wire covers 8b, 8c are inserted into corresponding wire leading-out holes, and a trunk part 802 arranged closer to the other axial-end side of the wire leading-out hole (i.e., on an end side of the wire leading-out hole that opens on the motor-housing side) than the head part 801.