PURPOSE: To attach and detach chocks on the operating and driving sides through hydraulic drive only at the same time, to remove a sling work and to improve safety and efficiency by equipping a truck on the driving side provided with a device for attaching and detaching the chocks so that it can slide freely in the direction of the roll shaft of a roll support device.

CONSTITUTION: A hydraulic truck 31-1 for the chock and a truck 41 for attaching and detaching a coupling are connected as the same elevating truck to attach and detach chocks 2-1, 2-2 and the coupling 3 by one running truck. Further, as a fine controller to the coupling 3 and a roll neck fitting part, a roll rotating device, a hydraulic motor are equipped in the peripheral direction and a function of high and low speeds is given to the truck so that equipments such as a coupling detaching device 41, a running truck are not damaged by unreasonable force based on interval differences between coupling fitting parts and the working efficiency is improved. Further, in the chock detaching device, guide rolls and side rolls are mounted at both ends of the rails for the running truck.