To enable producing without the need for an extension step of an outer body while being excellent in a fit of the edges around the legs. The above problem is solved by an underpants-type disposable diaper wherein an inner body (200) is joined to a crotch side edge portion of a central portion in a width direction of a dorsal side outer body (12B) to form an inner body joined section (12Z), a front- back length of a side closer to a waist side than the inner body joined section (12Z) is extensible to a crotch side, and the side closer to the waist side than the inner body joined section (12Z) in the inner body (200) can be moved to the crotch side, relative to a dorsal side outer body (12B).
