There are provided an optical disc 5, a cartridge body 6, a recording-reproducing opening 21, a shutter plate 25, and a shutter open/close mechanism 26. The cartridge body 6 has a disc container 16 for accommodating the optical disc 5 therein. The recording-reproducing opening 21 is provided on the cartridge body 6 for externally exposing part of a recording area of the optical disc 5 ranging from an inner periphery to an outer periphery. The shutter plate 25 is provided for opening and closing the recording-reproducing opening 21. The shutter open/close mechanism 26 has a guide groove 34 for movably supporting the shutter plate 25. The guide groove 34 is provided obliquely with reference to a width direction of the cartridge body 6 on the principal plane thereof.