To prevent collision of a disk and the internal surface of a cartridge body without increase of thickness of the cartridge body by suppressing inclination of the disk within the cartridge body.

A projecting portion 8 being projected toward an upper half 7 of a cartridge body 2 is provided at the rotation center of a center hub 4 holding the center area of a disk 3 accommodated to rotate within a cartridge body 2. Simultaneously, a projecting portion 14 for pressing the disk 3 toward the lower half 7 of the cartridge body 2 is provided to a shutter member 5 having the rotation center at the position different from the rotation center of the center hub 4, in contact with the projecting portion 8 provided at the center hub 4 when the shutter member 5 closes an aperture for entry of magnetic head.