PURPOSE: To improve rust preventing effect of a surface to be coated comprising a magnetic body impressed by magnetic field by allowing coating film to contact closely with the surface to be coated and coating a specified coating meterial contg. a magnetic body.

CONSTITUTION: A paint 3 contg. filler 3A comprising a magnetic body is prepd. by mixing magnetic iron oxide with alkaline paint contg. hexavalent chromium. The paint 3 is applied to the surface 1 to be coated comprising a magnetic body, and magnetic flux Mf1 is formed simultaneously between an N pole and an S pole of a magnet 2 by allowing the magnet 2 to contact with the surface 1 to be coated. Thus, the coating film is formed with close contact with the surface to be coated, so rust preventing effect is improved.