PURPOSE: To enable loading and unloading in a safe and narrow space because of no projection to the outside of a load box in the case a rear door of the load box of a truck is opened and closed.

CONSTITUTION: Guide rails are provided on upper and lower parts of the rear of a load box and those parts of a side wall of the load box. After 90° is bent from the rear of the load box, the rear door sliding forward along the side wall of the load box is formed of a plurality of separated building panels 5. Panel bearing boards 7 are provided to upper and lower parts of the panels 5, the guide rails are held from the insides and outsides to the panel bearing boards, and an inside holding roller rotating in a horizontal direction and an outside holding roller 9 are provided. A guide roller 11 rotating on the guide rails is provided to the panel bearing board of the lower part of the panels. Chains 15 mounted to bearing pins of the outside holding roller are connected to upper and lower parts of the panels.