To actualize an illegal use prevention system which allows a regular user to use a floppy disk and can surely prevent it from being used illegally.

Two pieces of data whose calculation result indicates the volume serial number of a regular floppy disk are written to storage parts 220 and 230. The data written to storage parts 240, and 220 and 230 are read by read parts 140, and 110 and 120 respectively, a calculation part 130 performs calculation, and a comparison part 140 makes a comparison. When, the comparison result shows a discrepancy, a following setup processing is quitted. When an all-sector copy is taken, the volume serial number is also copied and illegal use can not be prevented by this method, so a bad sector part 210 is generated as a countermeasure. Thus, the all-sector copying processing itself is made to end in failure, thereby disabling the illegal copy.