PURPOSE: To unifomalize an air current passing through each air pasage, improve the capacity of a fan and reduce the noise produced by a constructon wherein a cross section area pertitioned by a mount for an electric motor and that partitioned by a guide vane are made roughtly equal.

CONSTITUTION: A cross section area partitioned by a mount 3 for an electric motor 2 and a support 4, and those of air passageways 9 and 10 partitioned by a casing 1, and electric motor 2, a mount 3 and guide vane 7 are made approximately equal. Therefore, a flow near a bell-mouth on the blow-in side of the casing 1 is a uniform flow close to a laminar flow, bur an air current in the rear sent by a fan 5 on the blow-in side uniformly flows into a fan 6 on the discharge side since the cross section areas of the air passageways 8, 9, 10 partitioned are equal. As a result, air flows into the fan 6 on the discharge side in such condition as has been designed, and the characteristics and flowing condition of the fan 6 on the discharge side are improved, the generation of noise being reduced.