PURPOSE: To generate a magnetic flux in the void through which a material to be filtered is passed by isolating each magnetic particle with a nonmagnetic body.

CONSTITUTION: Each magnetic particle is kept out of contact with each other by mixing particles or small pieces in the forms other than a sphere of a magnetic body such as a ferrite magnet with particles or small pieces consisting of a nonmagnetic substance such as a ceramic. Namely, particles consisting of a magnetic and a nonmagnetic body are mixed with a binder, and the mixture is sufficiently agitated, charged into a specified metallic mold, compression-molded, and heated to a temp. at which the contact parts of the particles are welded to finish the calcination. Then the material is cut into a specified shape or polished, etc., and finally magnetized to obtain a porous filter having magnetism.