PURPOSE: To simplify a manufacturing process and to achieve a mass production system by cutting a top sheet along both side edge lines of the wide part of the top sheet and the front and rear edge lines of the narrow part thereof and folding back the top sheet along the side edge lines of the narrow parts to integrally form a pair of left and right erected elastic sheet materials and top sheet materials having pleat parts and double elastic parts.

CONSTITUTION: A nonwoven fabric 2A' for forming top sheet 2 is formed so as to have a width l' larger than the lateral width (l) of a product. The top sheet 2 is cut along both side edge lines S/a of the wide part of the top sheet 2 and the front and rear edge lines S1b, S1c of the narrow part thereof to form a pair of left and right erected elastic sheet materials 1A and top sheet materials 2A having pleat parts 11 and double elastic parts 12. The materials 1A are folded back along the side edge lines of the narrow part of the top sheet to oppose the materials 1A to the upper surfaces of the materials 2A. A back sheet material 5A having an absorbing pad 6 connected thereto is supplied to be adhered to the top sheet materials 2A. Next, the materials 1A, 2A are cut into a predetermined dimension along with the back sheet material 5A to form a disposable diaper having an erected elastic sheet 1.