To prevent the damage of a ball bearing of a ball bearing spindle motor mounted on a magnetic disk device of a loading/unloading system by providing the spindle motor with a mechanism capable of maintaining the stop state of a magnetic disk even while the magnetic disk is under stoppage of rotation.

The magnetic disk device of the loading/unloading system is provided with a locking means (for example, a dummy head 110) for maintaining the rotation stoppage state of the spindle motor 13 when the rotation of the substrate is held stopped by accompanying the drive stop of a spindle motor drive means.