PURPOSE: To simplify a debugging work by converting a data string recorded on a reproduction-only optical disk to a format at the time of recording on a reproduction-only optical disk and recording it on a recordable and reproducible magneto-optical disk.

CONSTITUTION: The data strings recorded on the reproduction-only optical disks 28, 40 are converted to the format at the time of recording on the reproduction-only optical disks 28, 40, and conversion data are made, and the data are recorded on the recordable and reproducible magneto-optical disk 4. Then, the behavior at the time of reproducing the data string recorded on the disks 28, 40 is confirmed by the disk 4. At this time, a parity sector is allocated, and the recording area of the data line is formed, and a control track and a DDS area are formed on front and rear of the recording area of the data string. Thus, debugging is processed easily, and a stamper is formed easily and surely after the debugging is processed.