PURPOSE: To make air-water separation securely to keep suction head and increase water feeding performance by providing a protruded portion for leading water stream to a discharge port on a discharge side of a final-stage guide wane and also providing a counterflow wall on the flow-out side of the uppermost portion of a guide vane.

CONSTITUTION: A final-stage impeller 22 and a pre-stage impeller 23 are connected to a shaft 21 of a motor 20 by nuts and stored in a pump casing 27. In the pump casing 27, a projected portion 36 is provided at the side of a compartment 30 formed by a partition 29 formed integrally with a final-stage guide vane 28 and the outer periphery of the pump casing 27, and a counterflow wall 37 is provided at the flow-out side at the uppermost of a guide wane 28b of a final-stage guide wane 28. Thus flowing speed at the periphery is suppressed by the protruded portion 36 to prevent turbulent flow and flow is directed against the counterflow wall 37 and led into the chamber to form upflow and make gas-water separation, whereby pressure drop can be prevented.