The present invention offers a simple structure that facilitates the mounting of bearings, that maintains lubricating oil at a sufficient level in the bearing portions and that maintains an optimal distance between a rotor and a case housing for preventing freezing, for preventing reduction of the capacity and for preventing noise. Bearing stoppers provided between the bearings of the brushless motor and the bearing holders, which hold the upper end edge of each bearing, are secured at a projection formed at the internal circumferential surface of each bearing holder. A felt, which comes in contact with the lower portion of each bearing stopper and also comes in contact with the bearing at one side is provided, with holes communicating with the felt formed at the lower surface of the bearing stopper. In addition, the lower limit of the distance h between the lower end of the rotor and the upper end surface of the case housing is set at 1.5 mm. This prevents water from forming a connection between the rotor and the case housing due to capillary action and surface tension. In addition, the upper limit of the distance h is set at or under 8 mm, which represents the critical point for the capacity and the noise. This ensures that the capacity is maintained at a satisfactory level and also prevents noise from increasing. Moreover, a washer group, which comprises at least one each of a resin washer, a rubber washer and a POM (polyoxymethylene) washer is provided between a sensor magnet that is secured to the lower end of the rotating shaft and the lower bearing.