PROBLEM TO BE SOLVED: To achieve both prevention of reduction in air permeability and prevention of fastening traces of a slender elastic expansion member.SOLUTION: An expansion structure of an absorbent article comprises: a sheet-like member 12S made of an air-permeable material and including a pleat 80 protruding to the opposite side to a skin contact side and a cover part 85 overlapping on the skin side of the pleat 80 while the pleat 80 is laid down and a slender elastic expansion member 90 provided along a longer direction of the pleat 80 between facing surfaces 80a, 80b of each pleat 80. The elastic expansion member 90 is disposed so as to pass between a root part 81 and a tip part 82 of the pleat 80, and at least both ends of the elastic expansion member are fixed between the facing surfaces 80a, 80b of the pleat 80. The pleat 80 is fixed continuously or intermittently in an expansion direction of the pleat 80 so that the facing surfaces 80a, 80b at the root part 81 are not separated from each other. Due to the contraction of the elastic expansion member 90, the pleat 80 and the cover part 85 contract respectively, and wrinkles are formed respectively.
