To restrain variation in the axial position of a rotating member within a range to make a device set in the rotating member normally function.

In mounting a sun gear 31 and a rotor shaft 36, the outer peripheral surface of a projecting part 90 of the sun gear 31 and the inner peripheral surface of a skirt part 91 of the rotor shaft 36 are gear spline-coupled at a connecting part 92, a snap ring 70 is disposed between a shoulder part 93 of the sun gear 31 and the tip of the skirt part 91 of the rotor shaft 36, and a clearance gap between the tip of the projecting part 90 of the sun gear 31 and the bottom 94 of the rotor shaft 36 has a width L1. The width L1 is smaller than the width L2 of a snap ring 70 and the width L3 of a thrust bearing 72, and smaller than the moving width to disable a resolver 80 from operating normally when the rotor shaft 36 is moved in the direction of the sun gear 31. As a result, the variation in the axial position of the rotating member can be restrained within a range to make the device set in the rotating member normally function.