To prevent metal powder from attaching to a motor by using a small magnet when a reduction gear and the motor which are coaxially arranged are sequentially lubricated and cooled by circulating oil by an oil pump.

The motor rotation is transmitted from a rotor 7 to a wheel 10 through an input shaft 8, a reduction gear 5, and an output shaft 9. A pump 31 is used to suck in oil within a space 34 and discharge the oil toward the reduction gear 5 from a hollow hole 8a and a radial hole 8b of the input shaft 8 so as to lubricate the reduction gear 5. After passing through the reduction gear 5, the oil arrives at an oil sump within a space 33 and heads toward an oil sump within a space 34 through an axial groove 36. In the meantime, the oil passes through a motor 4 and cools the motor 4. The metal powder mixed into the oil when the oil passes through the reduction gear 5 is attracted by a magnet 37 in an upstream side connecting opening 36a of the axial groove 36. Thus, the small magnet 37 can prevent the situation in which the metal powder is continuously mixed into the circulating oil and attached to the motor 4.

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