A soft magnetic film is formed of a CoFeNi alloy containing trace amounts of chlorine and sulfur as impurities. The stress of the soft magnetic film can be reduced effectively, specifically to 1,200 MPa or less, by adjusting the concentration ratio of chlorine to sulfur within the range from 1 to 60. In addition, variations in film stress can be reduced to provide higher yields of CoFeNi alloy films with low stresses.