PURPOSE: To hold a semi-permanent corrosion-preventing effect with neither external power supply nor sacrifice electrode required by supplying a current, induced in a piezoelectric material by a pressure of driven fluid, to an electrode provided in a corrosion-preventing objective location of a fluid machine.

CONSTITUTION: An impeller 6 is driven to be rotated through a main shaft 5 by a drive source, to suck/deliver a driven fluid from a suction bell 3, and the fluid is delivered to a lifting pipe 1 from a bowl 2 to perform pumping through the lifting pipe 1. Here, a piezoelectric material 8 provided in an internal side surface of the lifting pipe 1 receives a pressure of the driven fluid 7 to induce a current, and since the induced current flows in an electrode 9 through a regulator 10 to move electric potential of a corrosion-preventing objective location of the lifting pipe 1 to an inactive region or passive state region, a semipermanent corrosion-preventing effect can be taken with no external power supply required.