PURPOSE: To obtain light and small-sized hinges with a simplified structure by providing a plurality of L-shaped hinge members on the side edge of a bottom borad and the lower edge of a side drop door in the load box mounted on a truck, and combining one pair at least in the opposite direction to other pairs among them.

CONSTITUTION: Almost L-shaped hinge members 5,... are fixed on the lower edge of a side drop door 4 of a load box 1, and combined with almsot L-shaped hinge members 3 provided on the side edge of a bottom board 2 of the load box 1 to face to them for forming hinges 6,.... At this stage, the frontmost hinge members 3', 5' are fixed in the opposite direction to other hinge members 3,... and 5,... and the hinge is fitted in the reverse direction. This construction permits to reduce the number of parts, simplify the work of assembly, and obtain a simple structure.