A disk drive is provided which uses a disk cartridge having an inner case for holding an optical disk; an outer case for accommodating the inner case, having an opening allowing the inner case to come in and out; a locking mechanism for locking the inner case in the outer case, provided in a vicinity of the opening; and a coupling mechanism for coupling the disk cartridge with another disk cartridge. The disk drive includes a mechanism for pulling out the inner case to a pulled-out position from the outer case by more than a half of the inner case but not by entirety thereof; a mechanism for holding the inner case at the pulled-out position and rotating the optical disk; and a mechanism for reading/writing data on the optical disk.