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 is joined to a crotch side edge portion of a central portion in a width direction of a dorsal side outer body to form an inner body joined section, a front-back length of a side closer to a waist side than the inner body joined section is extensible to a crotch side, and the side closer to the waist side than the inner body joined section in the inner body can be moved to the crotch side, relative to a dorsal side outer body.
