A disc cartridge has a cartridge body (2) formed with an aperture (6) for exposing at least a part of the signal recording area of an accommodated disc (1), and a shutter (9) slidably mounted on the cartridge body (2) to open or close the aperture (6). The cartridge body (2) is provided with a shutter opening groove (18) extending along the sliding direction of the shutter (9) which is parallel to the direction (L) of insertion of the disc cartridge (2) into a recording and/or reproducing apparatus to record and/or reproduce information signals on or from the disc, and a mistaken insertion inhibiting groove (19) extending parallel to the shutter opening groove (18) and having a length (G) shorter than the length (F) of the shutter opening groove (18). Mistaken insertion of the disc cartridge may be inhibited by mistaken insertion inhibiting pins (52, 53) provided in the recording and/or reproducing apparatus for mating with each of the grooves (18, 19).