A disc cartridge of a three-piece structure capable of being kept from being caught in an information recording/reproducing apparatus during loading/unloading thereof with respect to the apparatus. The disc cartridge includes an upper plate, a lower plate, and a center frame arranged between the upper plate and the lower plate, which are joined to each other to form a casing in which a disc-like medium is received. The upper plate defines the whole upper surface region of the disc cartridge, whereas the lower plate defines the whole lower surface region of the disc cartridge. The disc cartridge also includes an engaged structure in which an engagement structure of the information recording/reproducing apparatus is engagedly fitted. The engaged structure is constituted by only the lower plate.