A disc cartridge is provided. The disc cartridge includes an optical disc and a main cartridge body unit rotatably housing the optical disc. A lateral surface of the main cartridge body unit as an inserting end of the main cartridge body unit into the recording and/or reproducing apparatus is a semicircular arcuate section having the center of the optical disc accommodated in the main cartridge body unit as center. The direction of insertion of the main cartridge body unit into the recording and/or reproducing apparatus may be discriminated readily to achieve smooth loading.