An extensible composite member (1) including an extensible portion (10) having two sheet materials (2, 3) and elastic members (4) intermediate between the sheet materials. The two sheet materials (2, 3) are discontinuously bonded to each other in the extending direction of the extensible portion (10) (X direction) and a direction perpendicular thereto (Y direction). The elastic members (4) are arranged in the extensible portion (10) avoiding joints (5) between the sheet materials and have both ends thereof fixed to the sheet materials. Each of the two sheet materials (2, 3) forms folds (6) continuously running across a plurality of the elastic members (4).