PURPOSE: To make compact by providing a projected/recessed band for pumping out from the inner to the outercircumference on the surface of a disc at the flow-in path side while providing a projected/recessed band for pumping in from the outer to the inner circumference on the surface at the delivery side.

CONSTITUTION: A casing 3 for containing a disc 1 is provided with a suction port 4 and a delivery port 5. First projected/recessed band 6 is formed with a groove partitioned by the curves (b), (c) and the remaining section on the surface of said disc 1 at the suction port side while second projected/recessed band 7 is formed in the opposite direction from said band 6 on the other surface or the surface at the delivery port side. Consequently, a small hydraulic pump can be obtained by simply rotating single disc in the casing.