PURPOSE: To reduce blowing loss due to an irregularity in rotating speed and to stabilize performance by forming the shape of an inlet of the air of an air guide in a semicircular shape, and forming the sectional area of its end in a streamline shape.

CONSTITUTION: An air guide 27 for holding the load side bearing of a rotor 21 is provided under a stator 25 and a fan 28 rotating together with the rotor 21. The guide 27 is formed in a semicircular shape at an air inlet 27a as shown, in the figure and the section of the end is formed in a streamline shape. Thus, the flowing line of the air to be discharged from a fan is varied according to an irregularity in the rotating speed of the fan. Even if its angle is varied, the shape of the inlet of the air of the guide is formed in the semicircular shape. Accordingly, the flowing axis of the air is always introduced perpendicularly to the inlet, and since the end of the inlet is formed in the streamline shape, loss of blowing at the inlet is reduced.