An apparatus for clamping a hard disk includes a motor rotating body having a boss inserted in a central hole of the hard disk and having a threaded portion formed on an outer circumferential surface of the boss and an accommodation surface supporting part a lower surface of the hard disk, a clamping washer inserted around the boss of the motor rotating body and placed on an upper surface of the hard disk, and a clamping nut placed on the clamping washer and coupled to the threaded portion of the boss so as to clamp the hard disk between the clamping washer and the accommodation surface of the rotating body.