A disk cartridge does not require a plate supporter for holding a chucking plate on an upper shell. In this disk cartridge, a chucking plate for chucking a disk on a turntable, driven by a spindle motor, is placed on the middle of the disk so the chucking plate is vertically movable together with the disk. The disk cartridge further includes a peripheral cylindrical rib which is not in contact with the disk and is configured to limit movement of the chucking plate in the direction of its diameter while permitting the vertical movement of the chucking plate. The peripheral cylindrical rib is molded integral with the lower surface of the upper shell.