Recording disk apparatus and clamp therefor

A recording disk apparatus comprises a recording disk supported by a rotation axis. A clamp is fixed at the tip end of the rotation axis by screws so as to urge the recording disk against a flange at the base end of the rotation axis. The screws are disposed along an imaginary circle concentric to the rotation axis so as to fix a plane body of the clamp at the tip end of the rotation axis. A rigidity reduction mechanism reduces rigidity of the plane body at an intermediate area relative to screw bore areas, which intermediate area defined between the screw bore areas along the imaginary circle. The rigidity reduction mechanism serves to suppress the undulation of the magnetic disk.