An absorbent article , comprising: an absorbent main body including an absorbent core having a longitudinal direction and a lateral direction intersecting each other; and leak-proof walls in a pair respectively provided on both sides in the lateral direction of the absorbent main body, the leak-proof walls including elastic members that are stretchable in the longitudinal direction, the absorbent core including a concave portion that is concave inward in the lateral direction in the central portion in the longitudinal direction, a dimension in the lateral direction of the concave portion provided in the absorbent core being smaller than a dimension in the lateral direction of both ends in the longitudinal direction of the absorbent core, the leak-proof walls each including a joining part where portions of a surface of each of the leak-proof walls are joined to each other on one side in a thickness direction, the leak-proof walls each including a non-joining part in at least one of a region on one end side and a region on another end side in the longitudinal direction with respect to the joining part , the non-joining part being where portions of a surface of each of the leak-proof walls are not joined to each other on the one side in a thickness direction, the joining part provided in each of the leak-proof walls in a pair not overlapping the absorbent core in the thickness direction, a distance (W50) between the joining parts provided to the leak-proof walls in a pair being greater in the lateral direction than a minimum dimension of the concave portion and smaller in the lateral direction than a dimension of both the ends in the longitudinal direction of the absorbent core. an absorbent main body including an absorbent core having a longitudinal direction and a lateral direction intersecting each other; and leak-proof walls in a pair respectively provided on both sides in the lateral direction of the absorbent main body, the leak-proof walls including elastic members that are stretchable in the longitudinal direction, the absorbent core including a concave portion that is concave inward in the lateral direction in the central portion in the longitudinal direction, a dimension in the lateral direction of the concave portion provided in the absorbent core being smaller than a dimension in the lateral direction of both ends in the longitudinal direction of the absorbent core, the leak-proof walls each including a joining part where portions of a surface of each of the leak-proof walls are joined to each other on one side in a thickness direction, the leak-proof walls each including a non-joining part in at least one of a region on one end side and a region on another end side in the longitudinal direction with respect to the joining part , the non-joining part being where portions of a surface of each of the leak-proof walls are not joined to each other on the one side in a thickness direction, the joining part provided in each of the leak-proof walls in a pair not overlapping the absorbent core in the thickness direction, a distance (W50) between the joining parts provided to the leak-proof walls in a pair being greater in the lateral direction than a minimum dimension of the concave portion and smaller in the lateral direction than a dimension of both the ends in the longitudinal direction of the absorbent core. <EOS>