PURPOSE: To reduce a turbulent vortex due to an effect of a flange so as to reduce noise by cutting the outer peripheral shape of a fan blade by a line connecting a predetermined point at the end in the rotating direction of the blade to another predetermined point inside a radius at the end.

CONSTITUTION: A motor 4 is supported at the center of an air duct by a plurality of support legs 2 disposed at the end on an air discharge side of a hollow and cylindrical venturi case 1. A plurality of fan blades 3 planted in a rotor hub of the motor 4 is housed in the air duct. The tip of the fan blade 3 is cut on a straight or arcuate line connecting a point A apart by a length W' of 20-30% of an arcuate length W from the tip in the rotating direction to a point B of 90-95% of a radius at the front edge in the rotating direction, thus obtaining a shape 9. Since a clearance between the inner circumferential surface of the air duct 1 and the tip 13 in the rotating direction of the fan blade 3 is enlarged in a tapered manner, it is possible to restrain a turbulent vortex generated by an air flow toward the air duct 1 so as to reduce noise.