PURPOSE: To form oxidized film without variance of oxidation degree on the surface of the titled powder, by a method wherein organic solvent is made to be a specified mixed solvent in the titled method where iron base metal powder dipped into organic solvent is dried in the gas involving O2.

CONSTITUTION: Iron or iron alloy powder is, in a dipping manner, processed with the mixed solvent composed of organic solvent inactive to those powder and the organic compound having higher boiling point than that of this organic solvent, being compatible therewith, and further being inactive to the titled powder. Oxidized film is formed on the surface of this wetting magnetic powder by evaporating organic solvent in the gas involving O2. At that time, a width generates in the boiling point of solvent and the speed of evaporation decreases as time passes, if conditions such as temperature, humidity, gas flow amount, etc. of atmosphere are constant. Thereby uniform and minute oxidized film is formed on the surface of magnetic powder and organic compound having high boiling point is adsorbed on its surface at the same time.