PROBLEM TO BE SOLVED: To provide an underpants-type disposable diaper adjustable in a leg peripheral size.SOLUTION: This underpants-type disposable diaper includes inner outer junctions 71 and 72 which join each an overlapping part of an internal body 200 and an external sheet 12F of an abdominal side, and an overlapping part of the internal body 200 and an external sheet 12B of a back side. The inner outer junctions 71 and 72 of the abdominal side and the back side are a non-peelable junction 71 preventing the end part of a waist side from peeling off, and the external sheet of a side including a peelable junction is provided with a marginal-part-detaching perforation for detaching the marginal part of a crotch side over the entire width direction.
