An electromagnetic filter includes a filtering column filled with a magnetic material and an electromagnetic coil disposed around the filtering column. The magnetic material comprises a plurality of cylindrical, prismatic or plate-like masses of magnetic material placed horizontally in the filtering column so as to form a plurality of layers, each of the masses of magnetic material consisting of a multiplicity of magnetic wires or magnetic tapes bundled so as to have their longitudinal axes arranged in substantially in parallel.The magnetic material filling the filtering column is distributed to a uniform density, so that impairment of the treating effect due to channeling of feed water through sparse portions of the magnetic material and the insufficient washing of dense portions thereof during the cleaning operation for expelling the magnetic particles entrapped in the magnetic material can be avoided. The efficiency of the electromagnetic filter is enhanced because all of the magnetic material filling the filtering column effectively participates in the entrapment of magnetic particles suspended in the feed water.