A cartridge for encasing optical discs of different diameters and thus permitting to load bare optical discs of different diameters into a disc cartridge-dedicated recorder/player. It includes a cartridge body (2) formed from an upper shell (6) having formed therein an insertion/removal opening (2a) for a first optical disc (3a) and a lower shell (7) having a write/read opening (24) formed therein, the upper and lower shells (6, 7) being butted to each other, a middle shell (4) having formed in the main side thereof an opening (44) corresponding to the opening (24) and which is rotatably received in the cartridge body (2), and a pair of shutter members (5a, 5b) installed on the middle shell (4) at the side of the lower shell (7) and which uncovers the openings (24, 44) when the middle shell (4) rotates until the openings (24, 44) are aligned with each other. A disc receptacle (11a) is formed to have a disc holder (11b) in which the first optical disc (3a) is rotatably held and a disc holder (11c) in which a smaller-diameter second optical disc (3c) is rotatably held.