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 (20) is formed by stacking an elastic sheet layer (30) between a first sheet layer (20A) and a second sheet layer (20B), when the elastic sheet layer (30) is extended in a width direction, the first sheet layer (20A) and the second sheet layer (20B) are joined together directly or indirectly at a large number of dot-like joint portions (40) arranged at intervals left in the width-direction and front-back direction, cover parts (C) of the outer body (20) of a back body (B) have peripheral edge regions (71) and surrounded regions (72) surrounded by the peripheral edge regions (71), and the arrangement density of the dot-like joint portions (40) in the peripheral edge regions (71) is higher than the arrangement density of the dot-like joint portions (40) in the surrounded regions (72).
