A disk clamp of a hard disk drive installs a disk firmly for storing data using a spindle motor of the hard disk drive. The disk clamp includes a vertical pressing portion, formed along an edge portion of the disk, for pressing an upper surface of the disk in a vertical direction, a plurality of horizontal pressing portions, formed inside the vertical pressing portion to protrude downward and be inserted between an outer circumference of the spindle motor and an inner circumference of the disk, to press an inner circumferential surface of the disk outwardly, and a plurality of screw coupling holes formed inside the horizontal pressing portion, through which screws are inserted to be coupled to an upper end portion of the spindle motor. The horizontal pressing portions are formed in at least three positions in a circumferential direction at regular intervals or at four positions at an interval of approximately 90.degree. in the circumferential direction. Thus, when an external impact is applied to the hard disk drive, a slip of the disk is not generated, and the spindle motor is prevented from being damaged.