Provided is a security system for managing which CD-ROM is used for a game device not having identifying information in advance. When a game device accesses a server via a communication network, a device ID, which is issued from the server, is stored in a nonvolatile memory This device ID is generated based on the time and date when the game device accesses the server via a communication network (e.g. Dec. 10, 2000 at 21:05:37). The server associates a serial number (SN) of a CD-ROM used in the game device and a device ID of the game device with each other and registers them on a database. This makes it possible to manage which CD-ROM is used in each game device.