Abstract: An optical disk includes a feature forming area 11 and a criterion recording area 12. The feature forming area 11 is an area provided with physical features used for determining whether it is an authorized optical disk or not. The criterion recording area 12 is an area having recorded therein the data of a determination criterion, i.e., a criterion by which it is determined whether the optical disk has been produced in an authorized manner or not on the basis of the physical feature. An optical disk reproduction apparatus detects the physical features provided in the feature forming area 11, and reads the determination criterion recorded in the criterion recording area 12. Furthermore, based on the determination criterion which has been read, the optical disk reproduction apparatus determines whether or not the detected physical features are those provided for an authorized optical disk.