PURPOSE: To make the film-forming condition wide and stable in the formation of an iron oxide thin film by sputtering using an iron target, by using Ar gas containing alcohol vapor for the oxidation reaction.

CONSTITUTION: The sputtering is carried out using a counter-target sputtering apparatus having a pair of iron targets placed oppositely to each other in a vacuum chamber, and placing a substrate e.g. a glass plate at the center of the chamber at a distance from the center line of the targets facing the treating face to the targets. The vacuum chamber is evacuated and filled with Ar gas, and the surface of the target is cleaned by applying DC sputtering voltage between the targets while shielding the substrate with a shutter. The vapor of CH3OH, C2H5OH, or CH3(CH2)2OH is introduced into the chamber without stopping the spttering operation, and the shutter of the substrate is opened to form an iron oxide thin film on the substrate.