A first bearing box has, in one end face perpendicular to a direction along a rotor shaft and farther from a fan, an air outlet for air taken in through an air inlet to exit. A flow channel is defined between an outer peripheral surface of a cylindrical portion of the first bearing box continuous with the end face and a frame. A value obtained by dividing a distance between an outer periphery of blades in the fan and the air outlet by an outer radius of the blades is greater than or equal to a threshold.