An optical disk master (19) having a diffraction structure including guide grooves (8) and small pre- pits (9) of a width narrower than a diffraction limit determined by a wavelength of light used is produced by preparing a photoresist layer (21) subjected to anti-dissolution surface treatment, narrowing the spot diameter of a zero-th diffracted beam irradiated on the photoresist layer by means of a super resolution optics (22), and effecting high contrast development to leave behind, as it is, a portion of the photoresist layer exposed to adverse higher order diffracted beams caused by super resolution. An optical disk (45) produced from the master has a diffraction structure including tracks and/or pre-pits formed along a spiral track or concentric tracks (7) and having a width narrower than a diffraction limit determined by a wavelength of light used in the course of formation of the diffraction structure.