PURPOSE: To enable the separation of iron powders, cast iron powders or the like from a filtered liquid during filtering action by magnetizing a filter main body constituted from a wire material or a plate material with plural pores made from permanent magnet.

CONSTITUTION: An inner and an outer surface side of a cylindrical filter main body 1 constituted from a net made from a permanent magnet wire material is magnetized to mutually opposite polarity. This filter main body 1 is mounted integrally in an inner side of a filter paper element 3 or mounted in a condition separated from a filter paper element 3 so as to surround the periphery of the said filter element 3 within a filter device and used. Or, a surface and a back surface of a filter main body 1' constituted from a net made from a permanent magnet wire material 2 are mutually magnetized to opposite polarity and this disc like filter 1' is mounted on an upper surface of a filter paper element 3 or mounted in the interior of a filter device 4' and used.