In a disc cartridge, the shutter opening/closing operation is to be performed reliably. To this end, the distal ends of a first engagement member 75 and a second engagement member 79 provided to a base 66 are pivotally movable in a direction along a lateral surface of a housing 51, in addition to being movable in a direction perpendicular to the lateral surface of the housing 51. The state of engagement of the first engagement member 75 and the second engagement member 79, provided to the base, with a first mating engagement section 110 and with a second mating engagement section 108, provided to an inner rotor 101, facing outwards from one lateral surface of the housing 51, when the base 66 performs relative movement along the lateral surface of the housing 51, may be maintained for prolonged time, while the load applied to the distal ends during engagement and disengagement may be reduced.