PURPOSE: To reduce work personnels, and shorten necessary time by fixing wires of respective winches arranged on both side of a lifter to a vessel, rewinding the wires according to a rise of the vessel by the lifter, measuring tensile forces of the respective wires and keeping them equal to each other when a posture is held, and keeping a difference in a rewinding length between the wires below an allowable value.

CONSTITUTION: A vessel S enters a dock in a condition where a platform 10 of a lifter and a carriage 7 above it are lowered, and the tips of wires 11a-14a of respective winches 11-14 are fixed to bollards 6 of the vessel S. After centering is performed by operation of the winches 11-14, they are set in automatic tension, and a zero point to display a wire rewinding length is adjusted, and an allowable value is set. The lifter is operated, and the vessel is raised, and a hydraulic motor 20 is controlled so that tensile forces of the wires are equalized to each other by respective tension gauges 17, and the wires 11a-14a are rewound by the respective winches 11-14. At the same time, the rewinding length is measured by a length detecting device, and a difference in the rewinding length is held and controlled below an allowable value.