At least an optical disk, a spindle motor, an optical head assembly and a seeking mechanism are mounted in a disk cartridge to accordingly establish a hermetically sealed structure. On the other hand, a disk cartridge guide member, an optical assembly, a disk cartridge lock mechanism, and an optical path switching mechanism are mounted in an optical disk drive. This enables the structure of improving the dust immunity of the disk cartridge and the low cost. Moreover, the optical disk drive can accommodate a plurality of disk cartridges. Thus, a disk cartridge implements a memory corresponding to various services. Or, an optical library of the present invention has mechanisms for mounting and detaching the optical disk cartridge accordingly accommodating a large number of disk cartridges in a limited space. Moreover, it is possible to provide an extremely small type of an optical disk drive to thereby design a memory unit applicable to various services including a portable apparatus. This is a media convertible storage system, which is superior in dust immunity and rapid access of a fixed magnetic disk and can record large-scale information and can satisfy various requests from miscellaneous application fields.