To efficiently remove scaly adhered substance such as calcium carbonate adhering to a filter element having a conductive filter part such as a metal spring.

In a filter 1, a plurality of the filter elements 6 are fitted to a partition member 3 in an electrical insulation state, and a power source unit 15 for supplying direct-current power supply to each filter element 6 is provided. By supplying the direct-current power supply to each filter element 6, an electrolytic deposit such as scaly substance adherent to the surface of each filter element 6 can be removed by an electrolytic action and washed.