| 摘要 |
PROBLEM TO BE SOLVED: To enhance the rigidity of a middle shell and to improve flatness by providing the middle shell with a rib part and changing the height of the rib part to various heights depending upon places. SOLUTION: The middle shell 25 of the disk cartridge having a cartridge casing 22, an optical disk 21 and a shutter mechanism 28 has a plane part facing one surface of the optical disk 21. This plane part is provided with an aperture 27 which is extended to the outer side in the radial direction from the approximate central part and opens to the outer peripheral edge, the inner rib part 39a which is extended to a circumferential direction in the segment corresponding to the non-recording region on the inner side in the radial direction of the optical disk 21, the outer rib part 39b which is extended to a circumferential direction in the segment corresponding to the nonrecording region on the outside in the radial direction of the optical disk 21 and the radial direction rib parts 39c and 39c which are extended along the edge segment extending in the radial direction of the aperture 27. The height of the radial direction rib part 39c is made lower than the height of the inner rib part 39a.
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