To surely prevent illegitimate reproduction by a CD-ROM driver and a CD-R/RW driver already existing on the market and attaining the ordinary reproduction operation itself of a program area as it has been in the past.

A flaw with a length of causing a read error is provided to both the end position of a lead-in area and the start position of a PMA (Program Memory Area) to prevent illegitimate reproduction. When a system controller 10 detects the flaw in reproducing the start position of a program area of the optical disk 1 and then reproducing the end position of the lead-in area, the system controller 10 reproduces the start position of a succeeding PMA without performing error processing, and when the system controller 10 detects the flaw in the case of reproducing the start position of the PMA, the system controller 10 starts reading of TOC (Table Of Contents) information from the start position of the lead-in area without performing error processing.