PROBLEM TO BE SOLVED: To expand the amount of telescopic motion of a width direction while maintaining suitable fastening in a section which has a fit elastic flexible member such as a hip.SOLUTION: The underpants type disposable diaper is characterized by forming a large flexible section EX in which the width of an inside and outside fixing part 301 which fixes an outer sheet 12 and an interior object 200 is narrower than the width of an inside and outside fixing parts 302 and 303 in front and back both sides EF and EB, and a waist lower elastic flexible member 15 and an intermediate part elastic flexible member 16 are extended to the side edge vicinity of the narrow width inside and outside fixed part 301, in a lengthwise range corresponding to a hip top part in a back bodice B.
