To provide an underwear type disposable diaper which is excellent in fit, which feels good to wear and which hardly slips down.

In the disposable diaper obtained by folding a disposable diaper constitution sheet material having an absorber 13 interposed between a liquid-permeable top sheet on a body side and a main body back sheet 20 covering an outer surface side so as to overlap a front section and a back section with a center part in a longitudinal direction as the position of a folding line and thermally melting and fitting both-side edges of the front section and the back section to form the underwear type, in the front section and the back section, body flap ES sections from the edge of a waist opening to nearly the upper edge of a leg opening are divided into three sections of a waist part section A, a side upper part section B and a side lower section C in order from the edge of the waist opening respectively, a plurality of elastic extensible members 23, 24, 25 and 27 are arranged along the width direction of the disposable diaper by each section, and elastic extension and contraction forces of each of the sections satisfy a relation of the side lower section C ≥ the side upper part section B > the waist part section A.