LIBRARY CONTROLLER

PROBLEM TO BE SOLVED: To perform a backup process irrelevantly to the use state of an optical disk stored in an optical disk library device by replacing an optical disk at a system information storage position with an unused optical disk unless the optical disk at the system information storage position is an unused optical disk. SOLUTION: When the use state of a backup magazine 1101 shows that the optical disk at the system information storage position is not an unused optical disk and an optical disk in the backup magazine constitutes the same volume, an optical disk replacement part 1209 replaces all the optical disks in a magazirne containing an unused optical disk with all optical disks put in the backup magazine 1101. At this time, the unused optical disk is stored at the system information storage position. A backup part 1208 uses the unused optical disk stored at the system information storage position.