A disc cartridge of a three-piece structure capable of enhancing moldability and rigidity of a center frame. The center frame having a square-like shape is interposedly arranged between an upper plate and a lower plate and has a receiving space defined therein for receiving a disc-like medium. The upper and lower plates are provided on four corners thereof with fixing bosses respectively. The center frame is formed on opposite surfaces thereof with fitting recesses in which the bosses are fitted, respectively. The center frame is formed on each corner thereof with a thin-wall portion having a reduced thickness of 50 to 80% based on a whole thickness of the center frame.