To provide a high discharge rate even in a high discharge pressure range.

A casing 18 is formed therein with a pump passage for returning fluid discharged from the outer peripheral side of an impeller 17 into a center side inlet port 27 of the impeller 17. Accordingly, fluid sucked into an inlet port 29 is led into the center side inlet port 27, and is subjected to energy obtained a pressure and a speed of a vane 22. Thus, the fluid is discharged from the outer peripheral side outlet port, and is then sucked into the center side inlet port 27. Since the fluid is circulated as mentioned above, the discharge pressure of the fluid becomes higher. Further, the vane 22 is spiral so that it is not orthogonal to the rotating direction thereof, and therefore, the fluid pressure does not greatly affect the vane 22 in the form of a load torque. Accordingly, even though the discharge pressure of the fluid becomes higher, the tendency of lowering the rotational speed of the impeller 17 can be restrained, thereby making it possible to ensure a high discharge rate.