To suppress the generation of noise by balancing the amount of suction with the amount of outlet upon low load and low head operation.

A main vane 9 is radially formed from a rotating shaft 11 with a clearance from the inner peripheral surface of a pump main body 1. A substantially triangular auxiliary vane 17 is provided below the rotating shaft 11. A drain guide part 18 having a cylindrical outer peripheral surface with an equal height is provided so as to be connected to the outer periphery of the main vane 9 and the auxiliary vane 17 with a clearance from the rotating shaft. On the lower surface of the drain guide part 18, an inverted conical surface part 19 is formed. On the upper surface of the guide part 18, an impeller 10 is provided which is connected to the upper surface of the outer periphery of the main vane and is provided with a ring shaped circumferential plate 21 having an opening between the rotating shaft and the impeller. The auxiliary vane comprises the substantially triangular part and a parallel part. The drain guide part has a plurality of guide surfaces successively inclined downward with respect to the rotating direction of the impeller. The inverted conical surface part is provided with a plurality of recessed parts toward the auxiliary vane side.