To effectively radiate the internal temperature of a driving motor, especially the bearing temperature so as to provide an axial flow fan, especially, an axial flow fan having a long lifetime.

This axial flow fan has a hollow rotor shaft 5 for pivotally supporting impellers 3, and a rotor hub 3-2 is provided with a small centrifugal fan structure having plural radiation impeller members 7-1 and plate-like side wall 7-2 in the peripheral surface of a side end of a bottom thereof. The rotor hub 3-2 is formed with a recessed part having a conical slope surface at the center of a bottom part thereof, and the small centrifugal fan structure 7 is housed in the recessed space, and the rotor hub 3-2 has plural flow aligning plates formed in the radiating direction continuously to the slope surface or a heating plate continuously provided to the slope surface of the conical recessed part in a surface of the bottom thereof.