PURPOSE: To effectively prevent the adhesion of slime to a sea water piping at a low cost by injecting an oxidant or sea water containing the oxidant, which is produced by bubbling natural sea water with ozone, into the sea water piping.

CONSTITUTION: Sea water 1 is pumped up with a water intake pump 2, and subsequently fed into a prescribed cooling installation through a sea water piping 3. Therein, the flow of the sea water is branched from the downstream side of the water intake pump 2 and subsequently fed into an oxidant-producing tank 6 capable of storing the sea water through a feeding valve 5. Ozone gas is injected from an ozone-generating device into the sea water-stored oxidant- producing tank 6 to produce the oxidant in the tank. When the concentration of the oxidant increases in the oxidant-producing tank 6 and reaches a prescribed concentration, a discharging valve 7 is opened and the oxidant-containing sea water is injected into the sea water piping 3 on the upstream side of the water intake pump 2 to prevent the adhesion of slimes to the inner wall of the sea water piping.