PURPOSE: To form concentric guide grooves in a simple constitution without using a mechanical method, by irradiating light to a photosensitive resin layer formed on a disk substrate via a conical solid and then applying a theory of an equal thickness interference.

CONSTITUTION: A photoresist is applied on the surface of a glass substrate 10 to form a photosensitive resin layer. The luminous flux given from a laser 15 is converted into parallel luminous fluxes through a collimator lens 18 and then made incident vertically to the substrate 10 from the bottom surface of cone 12 via a compensating filter 19 and a mirror 20. This incident light produces an equal thickness interference between a curved surface 22 of the cone 12 and the surface 21 of the photoresist 11, and the photoresist 11 is exposed with the light intensity corresponding to the interference fringes. Then a prescribed development process is applied to the photoresist to form concentric depressed and projjected parts in accordance with spaces of the light interference fringes. Then an optical recording layer is coated on the disk surface to obtain an optical disk for recording of information.