Disclosed is a locking controller mounted inside a sliding door. The locking controller is operated in connection with an inner handle resiliently returned to a neutral position when being turned into a door opening direction or into a door closing direction. If the inner handle is pulled or pushed in the door opening direction in the state that the sliding door is closed, the inner handle is turned into the door opening direction from the neutral position to release a door-close maintaining means. If the inner handle is pulled or pushed in the door closing direction in the state that the sliding door is open, the inner handle is turned into the door closing direction from the neutral position to release a door-open maintaining means. Therefore, a simple operation that the inner handle is turned in one direction makes the opening or shutting of the sliding door possible.