To prevent the load breakage or turnover during towing by operating an operation handle to the right or the left, and moving connecting rods connected to the handle to extend and contract the position of wheels.

This device comprises guide tools 6 containing wheels 5 provided on both sides of the wheel board 9 of a tractor and an operation handle 2 rotatable around a fixed immobile fulcrum 1 and provided in the center of the wheel board 9. It further comprises connecting rods 3 for connecting the handle 2 and the guide tool 6 in an equal distance, and the axles 7 of the wheels 5 built in the guide tools 6 are halved within an axle conduit 4 and smoothly moved. Auxiliary wheels 8 are provided to reinforce the axle 7 and the axle conduit 4 to the load applied thereto in the extension of the space between the wheels 5. When the wheel board 9 of the tractor is slightly lifted up to eliminate the grounding resistance, and the handle 2 is moved to the right, the two connecting rods 3 simultaneously extend the right guide tool 6 and the left guide tool 6 connected thereto, respectively, in the same manner to extend the side width space.