While an insulating film having a near-field light generating element placed thereon is being irradiated with light in an electrolytic solution, or after the film that has been irradiated with light is disposed in the electrolytic solution, a first voltage is applied between the two electrodes installed in the electrolytic solution across the film, a second voltage is then applied between the two electrodes, and a value of a current that flows between the two electrodes due to the application of the second voltage is detected. This procedure is stopped when the current value reaches or exceeds a pre-set threshold value, whereby a hole is formed at a desired location in the thin-film.