A disk cartridge which allows for the user to know what contents are recorded in which disk cartridge without the need of reproducing the disk cartridge, a method of manufacturing the same and a recording / reproducing system using the same have been provided, in which the disk cartridge is accomplished by incorporating the optical disk in a case, a recording surface of the optical disk is comprised of an annular inner area, a clamping area, a transition area, an information recording area and a rim area, which are arranged from inside to outside in radial directions of the optical disk, and disk cartridge identification information is recorded in the transition area of the optical disk, and also the disk cartridge identification information recorded in the optical disk is provided discernibly from outside the case.