Abstract: A mountable unit loading/unloading mechanism is provided for loading a hard disk drive unit into and removing a hard disk drive from an opening of a mount assembly. The loading/unloading mechanism includes a stationary plate secured to the hard disk drive unit, and a movable plate that has an elastically displaceable portion and can be slid with respect to the stationary plate in a direction of insertion into the mount assembly and in the opposite direction, which is a removal direction. When the hard disk drive unit is loaded into the mount assembly, the elastically displaceable portion is displaced outwardly and presses against the inner side walls of the mount assembly to lock the hard disk drive unit to the mount assembly.