An absorbent article comprising: an absorbent body having a longitudinal direction and a lateral direction orthogonal to each other; and a pair of leak-proof walls provided on both lateral sides of the absorbent body, each of the leak-proof walls formed of a sheet member including a plurality of first welded parts on a surface of the sheet member, characterised by each of the leak-proof walls including an overlaid part where the sheet member is overlaid in a thickness direction such that an elastic member stretching/contracting in the longitudinal direction is sandwiched, a plurality of second welded parts that join the overlaid sheet member disposed in at least a part of a region of the overlaid part, an area of the second welded parts being smaller than an area of the first welded parts, wherein an average value of thicknesses of portions, in the overlaid part, where the first welded parts are respectively formed is larger than an average value of thicknesses of portions, in the overlaid part, where the second welded parts are respectively formed, and an average value of thicknesses of portions, in a longitudinal central region of the overlaid part, where the second welded parts are respectively formed is smaller than an average value of thicknesses of portions, in a longitudinal end region of the overlaid part, where the second welded parts are respectively formed. an absorbent body having a longitudinal direction and a lateral direction orthogonal to each other; and a pair of leak-proof walls provided on both lateral sides of the absorbent body, each of the leak-proof walls formed of a sheet member including a plurality of first welded parts on a surface of the sheet member, characterised by each of the leak-proof walls including an overlaid part where the sheet member is overlaid in a thickness direction such that an elastic member stretching/contracting in the longitudinal direction is sandwiched, a plurality of second welded parts that join the overlaid sheet member disposed in at least a part of a region of the overlaid part, an area of the second welded parts being smaller than an area of the first welded parts, wherein an average value of thicknesses of portions, in the overlaid part, where the first welded parts are respectively formed is larger than an average value of thicknesses of portions, in the overlaid part, where the second welded parts are respectively formed, and each of the leak-proof walls formed of a sheet member including a plurality of first welded parts on a surface of the sheet member, characterised by each of the leak-proof walls including an overlaid part where the sheet member is overlaid in a thickness direction such that an elastic member stretching/contracting in the longitudinal direction is sandwiched, a plurality of second welded parts that join the overlaid sheet member disposed in at least a part of a region of the overlaid part, an area of the second welded parts being smaller than an area of the first welded parts, wherein an average value of thicknesses of portions, in the overlaid part, where the first welded parts are respectively formed is larger than an average value of thicknesses of portions, in the overlaid part, where the second welded parts are respectively formed, and an average value of thicknesses of portions, in a longitudinal central region of the overlaid part, where the second welded parts are respectively formed is smaller than an average value of thicknesses of portions, in a longitudinal end region of the overlaid part, where the second welded parts are respectively formed.