For corrugated cardboard boxes that are manually assembled, flaps may be folded outward to improve the packing process. In this case, since folding is done in a reverse manner, the repulsion is strong making it difficult to fold along the score line. At this point, we improved the packing process by facilitating reverse-folding with belt-like compression applied to the upper part of the score line of the flap to reduce the thickness of the corrugated cardboard resulting in less rigidity without lowering compressive strength.