It is an object of the invention to provide a disk cartridge having a substantially identical form to that of a disk cartridge that accommodates a disk-shaped recording medium having a first recording capacity and accommodating a disk-shaped recording medium having a second recording capacity, which is higher than the first recording capacity, wherein the disk cartridge includes a write protect mechanism, which is different from a write protect mechanism for the disk cartridge accommodating the disk-shaped recording medium having the first recording capacity.