PURPOSE: To prevent the efficiency of pump from degradation by providing a means for introducing water having pressure higher than that in an intake port from the outside of a casing into the central portion of the intake port and jetting said water.

CONSTITUTION: A casing flange 13 is provided with a recess 14 and a high pressure water path 15 communicating thereto, and a high pressure water path 17 communicating to a piping 16 and an intake port 3 are provided in an intake flange 2. High pressure water having pressure higher than that in the center of intake port 3, for example water discharged from a centrifugal pump is conducted to the path 15, piping 16, path 17 and jet 20 and jetted into C portion. Thus, pressure drop and pressure pulsation in the center of the intake port generated with swirling flow produced by reverse current from an impaller to the intake side can be securely prevented.