A disposable diaper includes a diaper body and a pair of side flaps each fixed to the diaper body at a fixing part and at least a joint part. The diaper body has transversely opposite side parts, each of which has opposite first and second end parts. The fixing parts and joint parts are located at the first end parts of the disposable diaper. Each fixing part is located inwardly of the respective joint part as seen in the width direction of the diaper body. Each side flap has an inner end part fixed to the diaper body and an outer end part to which a fastener is fixed.