A disk cartridge is provided. The disk cartridge includes a cartridge case including an upper shell having an inner circumferential wall and a lower shell having a first opening for recording and/or playback; an inner rotor rotatably disposed in the cartridge case and having a second opening corresponding to the first opening and an annular portion on the periphery thereof; and shutter members disposed between the inner rotor and the lower shell and rotatably attached to the inner rotor. The shutter members open the first and second openings when the inner rotor rotates so that the second opening agrees with the first opening. The inner circumferential wall of the upper shell is disposed inside the annular portion. The inner rotor has a groove opposite the leading end of the inner circumferential wall inside the annular portion. The groove has a width larger than the thickness of the leading end of the inner circumferential wall.