By combining outputs from a Hall sensor and a magnetoresistive sensor, a 360-degree rotary position sensor can be achieved. Each robot includes a manipulator, a control unit for automatically operating the manipulator, and a movable key device configured to store information about the identity of the robot to which the moveable key device belongs. The slots diverge outwardly so that as the handle is moved relative to the head the split aperture closes and the flexible head increasingly clamps a drive socket as more torque is applied to the handle. A cell discard controller discards a cell having a long elapsed time since the writing time stored in the writing time management memory by the processing, which is independent of the processing by the writing controller and the reading controller.