PURPOSE: To prevent the deviation between the main body of a magnetic disk and the center of a hub even if shock such as falling is applied on a magnetic disk having the hub structure for rotating the magnetic disk by pushing and fixing the magnetic disk with a clamping part from the upper side on the upper surface of an armature part, which is driven and rotated with a driving motor, with the magnetic disk being aligned with the center.

CONSTITUTION: A protruding part 1a is coupled into a central hole 3b of a magnetic disk 3. A clamping part 1 is coupled with an armature part 2 with a screw 4. A part, which is in contact with the entire surface of a chamfered part 3a around the central hole 3b of the magnetic disk 3, is provided in a part 1b of the clamping part 1, which receives the magnetic disk.