A disc cartridge having rotatably housed an optical disc (2) is disclosed. The disc cartridge includes a main cartridge body unit (5) having an aperture for the head part (13) for exposing a portion of the optical disc to outside across the inner and outer rims of the disc. In one surface of the main cartridge body unit is formed a center opening (12) into which is intruded a turntable (90) for rotationally driving the optical disc. An inner peripheral surface (81) of the center opening operates as a mounting reference plane along the planar direction when mounting the disc cartridge to a recording and/or reproducing apparatus. The rim of the opening of the one surface of the main cartridge body unit operates as a mounting reference surface (82) along the height-wise direction. The main cartridge body unit has an inserting end side into the recording and/or reproducing apparatus formed as a substantially semicircular arcuate section (7) having, as center, the center of the optical disc housed in the main cartridge body unit.