A process for preparing a soft magnetic film of Permalloy on a rugged substrate in an inert gas atmosphere by a multielectrode sputtering method wherein the target voltage and the target current are independently controllable, the Permalloy film being prepared by:(a) setting the inert gas pressure and the target voltage at values below the critical values where the coercive force of the Permalloy film abruptly increases when the film is formed on a flat substrate, and(b) applying to the rugged substrate during film formation a negative bias voltage not lower than a specific value determined by an angle of inclination formed by a stepped portion in the rugged substrate.