PROBLEM TO BE SOLVED: To suppress urine or feces from leaking out of a diaper.SOLUTION: A briefs type disposable diaper 1 which has one girth opening and a pair of thigh openings while the thigh areas defining the girth opening has extensibility and elasticity respectively includes a front portion 4F, a rear portion 4B, and a crotch portion 4C. When the diaper is spread, the front portion and the rear portion are longitudinally separated from each other, and the crotch portion longitudinally extends at a crossing-directional intermediate position and are joined with the front portion and the rear portion through a front joint area 6F and a rear joint area 6B respectively. The crotch portion is fitted with a side elastic member 5CS in an extended state along both its edge areas. The front joint area and the rear joint area include wide areas 6FW, 6BW provided around both longitudinal ends thereof and extending substantially overall in the crossing direction of the crotch portion, and narrow areas 6FN, 6BN provided between those wide areas and being narrower in the crossing direction than the wide areas.
