embodiments of the invention provide a clamping mechanism capable of clamping a magnetic disk by an accurate fastening force . in one embodiment , a magnetic disk fastening method includes the steps of : mounting a magnetic disk on a hub structure , setting a thin plate spring having a pressure - bearing part , a flexible part and a disk holding part at a predetermined position relative to the magnetic disk with the disk holding part in contact with a surface of the magnetic disk ; pressing the pressure - bearing part by screwing a fastening screw in a threaded hole formed in the hub structure ; measuring a deflection by which the flexible part is deflected in the pressure - bearing part pressing step ; and stopping pressing the magnetic disk upon the increase of the deflection to a predetermined value .