An impeller includes a disk-shaped hub and a plurality of vanes provided radially on the surface of the hub. The plurality of vanes are formed in a whirling pattern about the center of rotation of the impeller, and each of the vanes has an outer peripheral surface facing the inner peripheral surface of the volute. A rotational-direction rear end portion of the outer peripheral surface of each of the vanes has a recessed step surface formed thereon. The rotational-direction rear end of the recessed step surface of each of the vanes is formed to define an edge shape with respect to a rotational-direction rear end surface of the vane.