The present invention is intended to improve a fit to the lower part of a gluteal region. The foregoing issue is solved by an underpants-type disposable diaper in which an outer body is formed by stacking an elastic sheet layer between a first sheet layer and a second sheet layer, when the elastic sheet layer is extended in a width direction, the first sheet layer and the second sheet layer are joined together directly or indirectly at a large number of dot-like joint portions arranged at intervals left in the width-direction and front-back direction, cover parts of the outer body of a back body have peripheral edge regions and surrounded regions surrounded by the peripheral edge regions, and the arrangement density of the dot-like joint portions in the peripheral edge regions is higher than the arrangement density of the dot-like joint portions in the surrounded regions.
