To prevent a performance of an axial fan from reducing, and prevent non-repeatability of a performance by attaching a centrifugal impeller rotated together with an axial impeller so as to generate flow of a direction faced from a center of the axial impeller to an outside.

A centrifugal impeller 12 is attached on a surface of a disk 14 of a subsequent step of an impeller 1 for preventing a part of a fluid boosted up by a preceding step of the impeller 1 from leaking bypassing a clearance 21 between an inner cylinder 7 of a static blade part and the disk 14 of the subsequent step of the impeller 1. The centrifugal impeller 12 is attached on a suitable position of a diameter direction of a surface of the disk 14, and is positioned in the clearance 21. When the centrifugal impeller 12 is rotated together with the disk 14, flow is generated from a center (a rotary shaft side) of the disk 14 toward an outside (a moving blade side). The centrifugal impeller 12 is planed so as to equalize subsequent flow side pressure P1 of a preceding step of a static blade 3 and outlet pressure P2 of the centrifugal impeller 12 with each other. It is thus possible to prevent a performance of an axial fan from reducing by leakage flow, and it is also possible to prevent non- repeatability of a performance.