There are included a plurality of record information recording areas (OPC areas PCA0, user data areas 109-0 or spare areas SA) for recording record information; a management information recording area (management area MA) for recording a plurality of management information for managing the respective ones of the plurality of record information recording areas; and a reliability information recording area (management area MA) for recording a plurality of reliability information (reliability flag group 150) that indicate, for each of the plurality of management information (120, 130 or 140), reliability as to whether the plurality of management information are correctly updated.