Embodiments of the invention reduce disk fluttering while ensuring good assemblability in a magnetic disk apparatus. A magnetic disk apparatus comprises a recording disk that is an information medium configured by one or plural disks; a motor causing the recording disk to rotate; a carriage supporting a head that records information to, or plays back information from, the recording disk; a casing housing the recording disk; and a shroud disposed surrounding an outer periphery of the recording disk. A groove that extends along the recording disk is formed, vertically asymmetrical with respect to an outer peripheral surface of the recording disk, in the shroud surface at a position where a corner portion formed by the outer peripheral surface and a top surface or bottom surface of the recording disk extends in a radial direction.