An input means 4 is connected by way of a security check means 5 to a program data readout means 6. The program data readout means 6 is coupled to a game implementation means 11. To the security check means 5 are coupled a flag storage means 7 and an ID detection means 8. In the flag storage means 7 are stored a security flag 7a and a readout enabling flag 7b. To the ID detection means 8 are coupled an ID storage means 9 and an ID collation means 10. The ID collation means 10 is coupled to the program data readout means 6. A KEY-CD 2 stores an identifier KEY-ID 2b. A trial CD 1 stores an identifier DISC-ID 1 b. In response to the KEY-ID 2b detected from the KEY-CD 2, the security flag 7a becomes on, and after the collation of the DISC-ID 1 detected from the trial CD 1 with the KEY-ID 2b, the readout flag 7b becomes on. Then, the program data within the trial CD 1 are read out by the program data readout means 6, allowing the game implementation means 11 to execute a game. It is thus possible both to securely prevent the data stored in the storage medium from being illegally executed, analyzed. or copied by a person not having a legitimate title and to facilitate the execution of the data by a person having the legitimate title.