PURPOSE: To enable to automatically set bridging members simultaneously with the opening and closing of a rear gate by a structure wherein the bridging member slide down backward by gravity when the rear gate is open and return to their original states by gravity when the rear gate is closed.

CONSTITUTION: When a piston rod 9 is retreated under the state that the rear gate 2 is closed, the rear gate 2 is pivoted backward about a hinge 5. At this time, the bridging members 3 and 3' move downward and backward in such a manner as to slide down along the backward inclination of the rear gate 2. When the piston rod 9 is stretched under the above-mentioned closed state of the rear gate 2, the rear gate 2 is pivoted upward about the hinge 5 in order to be closed and the bridging members 3 and 3' are also pivoted upward integrally with the rear gate 2. Because the bridging members are automatically set simultaneously with the opening and closing of the rear gate in such a manner as mentioned above, the loading and unloading of cars are simplified.