A magnetic disk device having a cover of a simple structure having high rigidity and not easily deformable by pressure from the outside. An envelop surface configuration (46) of at least a portion of a cover (40) positioned opposite a magnetic disk (2, 43) is made generally conical, such that the distance from the magnetic disk decreases along a direction from the vicinity of a rotating shaft of a motor, as the center, toward the outer periphery of the magnetic disk, thereby reducing the amount of deformation of the cover, particularly in the vicinity of the rotating shaft of the motor.