Decrypting information corresponding to a selected track, file pointer information, and index information are read out from a track information table having the decrypting information corresponding to each track, the file pointer information showing one of a plurality of files with headers, and the index information showing a position in the file. The header of the file with the header is read out on the basis of the file pointer information and position information in the file corresponding to the index information is detected from the header. A part of data of the file is read out on the basis of the position information and the read-out data is decrypted on the basis of the decrypting information.