The purpose of the present invention is to provide a pants-type disposable diaper which achieves both a good fit on the intergluteal cleft and a good fit on portions adjacent to either side of the width of the intergluteal cleft. The above problem is solved by a pants-type disposable diaper which is characterized in that: at least an intergluteal cleft opposing portion (81) and portions (82) adjacent to either side of the width of the intergluteal cleft opposing portion (81) in an external body (20) of a back body portion (B) comprise a stretchable region (20X) that is stretchable in a width direction the stretchable region (20X) is an elastic film (30) stretchable structure which comprises an elastic film (30) that is laminated between a first sheet layer (20A) and a second sheet layer (20B), and in which, with the elastic film (30) extended in the width direction, the first sheet layer (20A) and the second sheet layer (20B) are joined directly or indirectly by multiple joining parts (40) that are arranged spaced apart from each other in the width direction, and a front and back direction and an area ratio of the joining parts (40) is configured to increase in a stepwise or continuous manner at least from the intergluteal cleft opposing portion (81) to the portions (82) adjacent to either side of the width of the intergluteal cleft opposing portion (81).Lobjet de la présente invention est de fournir une couche jetable de type culotte qui permet dobtenir un bon ajustement sur le pli interfessier et un bon ajustement sur des parties adjacentes à chaque côté de la largeur du pli interfessier. Le problème susmentionné est résolu au moyen dune couche jetable de type culotte qui est caractérisée en ce que : au moins une partie (81) opposée au pli interfessier et des parties (82) adjacentes à chaque côté de la largeur de la partie (81) opposée au pli interfessier dans un corps externe (20) dune partie de corps arrière (B) comprennent une région étirable (20X) qui est étir
