A disk cartridge comprising: an inner case for holing an optical disk; an outer case for accommodating the inner case, having an opening for allowing the inner case to come in and out; lock means for locking the inner case in the outer case, provided in a vicinity of the opening; and coupling means for coupling the disk cartridge with another disk cartridge. A disk drive using the disk cartridge comprising: a mechanism for pulling out the inner case 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 a position of being pulled out and rotating the optical disk; and a mechanism for reading/writing data on the optical disk. A disk changer apparatus comprising: a disk stacker for containing a plurality of the disk cartridges; the disk drive; and a mechanism for moving the disk drive device to a selected disk cartridge among the plurality of the disk cartridges.