When a program is activated, data recorded in a predetermined sector is reproduced by an error correction. When no reproduction error occurs, the data in the predetermined sector is reproduced without conducting the error correction. When reproduced data are not a predetermined pattern, it is determined that write software illegally writes dummy data to the predetermined sector, instead of the predetermined pattern, and an optical disc where the program is activated is a copied optical disc. Accordingly, a process conducted by the program is terminated. Therefore, a process realizing original functions based on the program cannot be executed.