PURPOSE: To reduce the amount of waste water, by eliminating a water flow swirling valve from a foreign matter removing device.

CONSTITUTION: The sea water containing foreign matter (a) fed in through a cooling water intake pipe 8 is fed to the first foreign matter removing device 21, where the foreign matter (a) is separated by a strainer 26, while clean water passes through the strainer 26 and is fed to a clean water outlet pipe 5. The sea water containing the foreign matter (a) flows into a waste water discharge pipe 22, and the foreign matter (a) is separated by a strainer 3 of the second foreign matter rmoving device 23. When the foreign matter (a) is accumulated on the inside surface of the strainer 3, a removing operation of the foreign matter is conducted. The water flow swirling valve 2 composed of two semicircular valves is set in the condition wherein the two valves are alternately inclined at a predetermined angle, so that a swirl is induced in the flow of sea water passing through the valve 2. Foreign matters such as seashells trapped on the inside surface of the strainer 3 is carried by the swirl flow and is directed to a cooling water discharge pipe 10 through the waste water discharged pipe 22.