An optical disk apparatus has a control portion for, based on address information and authentication information read out from an optical disk, providing access to a specific server via a communication line, thereby acquiring extensible information, and a reproducing portion for reproducing and outputting the acquired extensible information. In this optical disk apparatus, if an optical disk is not provided, authentication processing cannot be carried out, and extensible information cannot be acquired. Thus, extensible information can be reproduced with security.