To provide an underpants type disposable diaper that can be formed such that the edges of the leg openings fit the groin and gluteal portions of a wearer with no or less trim loss than conventional diapers The above problem is solved by that the ventral side outer sheet 12F and the back side outer sheet 12B each have a separated portion 12S formed by a slit or an elongated opening so as to extend in a width direction at a lengthwise middle section in a widthwise central region, a connecting member 12M connects the both outer sheets 12F, 12B at widthwise middle portions on the crotch side with respect to the separated portions, and the both outer sheets 12F, 12B are pulled up toward the waist side at entire widthwise sections on the waist side with respect to the separated portions 12S while being deformed with increased longitudinal separation distances of the separated portions 12S, and are diagonally pulled up toward the waist side at sections on the crotch side with respect to the separated portions 12S and at the same time, on both widthwise sides of connecting portions 12x connected to the connecting member, with increasing proximity to the both widthwise sides.
