PURPOSE: To reduce power consumption and prevent the occurrence of accidents at the time of interruption of water supply or power supply by a method wherein elements being magnetized and demagnetized are moved to a raw water treating part and a washing part, in a magnetic filter for removing magnetic corrosion products contained in feed water for a nuclear reactor and in reactor water.

CONSTITUTION: A conveyor 3 is operated to move the elements 11 made of a permanent magnet material in the direction of A11. The element 11 are magnetized by a magnetized by a magnetizing coil 4, and is stored in a filter main body 10 through a charging hopper. Then, raw water is introduced via an inlet port 6 and are passed through the main body 10, and the magnetic corrosion products contained in raw water are caught by the elements 11 by magnetic attraction. After the magnetic attraction is accomplished sufficiently, the supply of water is stopped, the elements 11 are discharged, a new charge of the elements 11 is placed into the main body 10 and filtration is restarted. The elements 11 thus discharged are demagnetized while passing through a demagnetizing coil 1, then the corrosion products are washed away by washing water at the washing part 2 of a regenerator 5, and the elements are served to reuse. Electric power is consumed only in magnetizing and demagnetizing.