PURPOSE: To obtain an optical disk having high-density guide grooves which are extremely stable by providing a heat resistant substrate, a guide substrate which is disposed on the main plane of the heat resistant substrate and has optical guides and a recording layer which is disposed on the guide substrate.

CONSTITUTION: The essential component of the photosensitive glass substrate 1 is silicate glass and is added with a slight amt. of metal such as Au, Ag or Cu and reducing agent such as CeO2 or Sb2O3 ad additives (metallic ions and sensitizer). The part irradiated with UV rays is, therefore, colored to have permanence. The optical disk is, thereupon, made usable in place of guide grooves by using the difference in reflectivity between the colored part and the uncolored part. The optical guides (black part and white part) are thereby easily formed at a high density while the high reliability is maintained.