To form cushioning materials to be applied along edges of an article out of corrugated boards.

Two pieces of outer plates 1 and 2 are connected with inner plates 4 and 6 provided at edges of the outer plates 1 and 2 respectively through edge plates 3 and 5, two pieces of tuck-in plates 8 and 9 are connected successively to the edge plate 5 on one side through a slant plate 7, both of the outer plates 1 and 2 are bent repsectively in an L-shape, the slant plate 7 is slanted by bending the slant plate 7 and the tuck-in plates 8 and 9 in a way of curling, the tuck-in plates 8 and 9 are laid respectively on the outer plates 1 and 2, the inner plates 4 and 6 are bent toward the inside, the tuck-in plates 8 and 9 are caught respectively between the outer plates 1, 2 and the inner plates 4, 6, and both of the inner plates 4 and 6 are engaged.