| 摘要 |
PROBLEM TO BE SOLVED: To hardly give rise to an offset in the centers of a small-diameter disk-like recording medium and an adapter during high-speed rotation and to allow stable recording and reproducing to be carried out. SOLUTION: Recording medium supporting parts 9 and 15 for supporting the small-diameter disk-like recording medium 5 are formed near an inner peripheral surface 8 of a recording medium supporting hole 6 of an adapter body 7. The recording medium supporting parts 9 and 15 are provided with upper supporting projections 10 for supporting one main surface 2 of the small- diameter disk-like recording medium 5 from above. Further, an inclined lower supporting inner peripheral surface 16 for supporting the outer peripheral surface 4 of the small-diameter disk-like recording medium 5 or the neighborhood of a corner part continuous with another main surface 3 from the outer peripheral surface 4 is formed. The region on the peripheral side outer than the upper supporting projections 10 of the adapter 7 is provided with long through-holes 13 or grooves and elasticity is imparted to the upper supporting projections 10 thereof to allow elastic deformation.
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