PURPOSE: To form film having excellent corrosion resistance without deteriorating magnetic characteristic by executing heat-treatment under vacuum or inert gas atmosphere after applying electropolishing to a magnet sintered body obtained by subjecting alloy powder containing rare earth group element, Fe and B as essential components to pressurizing, compacting and sintering.

CONSTITUTION: The rare earth group element-Fe-B series alloy powder compos ing of 8-30atm.% the rare earth group element containing Y and particularly the rare earth group element containing Nd, Pr and these mixed material, 2-25atm.% B and the balance of Fe, are pressurized and compacted to make the green compact. After making the sintered magnet by sintering this green compact, the surface is ground and successively submerged into the ordinary electropolishing liquid at -20 to +20°C, and the electricity is conducted at 0.01-1A/cm2 current density, and after electropolishing, the heat treatment is executed at 300-900°C under vacuum or inert gas. Passivating film is formed on surface of the magnet and the corrosion-proof effect of the magnet is im proved.