An underpants-type disposable diaper comprising: an outer body (12F, 12B) that has a ventral side outer part and a dorsal side outer part and a waist opening formed by joining side edge portions of the ventral side outer part and side edge portions of the dorsal side outer part at both width direction sides; and an inner body that has a front part joined to a width-direction central area of the ventral side outer part and a back part joined to a width-direction central area of the dorsal side outer part and passes through the crotch of a wearer, edges of leg openings (Le) being at least partially formed by edges of parts of the outer body (12F, 12B) positioned on width-direction both sides of the inner body, wherein in at least one of the ventral side outer part and the dorsal side outer part, parts at a lower edge of a side edge correspondence region corresponding to the side edge portions in a front-back direction, positioned on the both width direction sides of the inner body, constitute the edges of the leg openings (Le), a lower part of the side edge correspondence region is set as a folded part that is folded once or plural times in a zigzag manner in the front-back direction and fixed at the side edge portions, the folded part is gradually unfolded downward with increasing proximity to the width-direction central side, and the folded part is fixed in a halfway or completely downward unfolded state to the inner body at the width direction central portion, and elongated oblique resilient and elastic members are fixed in an extended state in a direction from the folded part to the side edges of the inner body below the folded part. an outer body (12F, 12B) that has a ventral side outer part and a dorsal side outer part and a waist opening formed by joining side edge portions of the ventral side outer part and side edge portions of the dorsal side outer part at both width direction sides; and an inner body that has a front part joined to a width-direction central area of the ventral side outer part and a back part joined to a width-direction central area of the dorsal side outer part and passes through the crotch of a wearer, edges of leg openings (Le) being at least partially formed by edges of parts of the outer body (12F, 12B) positioned on width-direction both sides of the inner body, wherein in at least one of the ventral side outer part and the dorsal side outer part, parts at a lower edge of a side edge correspondence region corresponding to the side edge portions in a front-back direction, positioned on the both width direction sides of the inner body, constitute the edges of the leg openings (Le), a lower part of the side edge correspondence region is set as a folded part that is folded once or plural times in a zigzag manner in the front-back direction and fixed at the side edge portions, the folded part is gradually unfolded downward with increasing proximity to the width-direction central side, and the folded part is fixed in a halfway or completely downward unfolded state to the inner body at the width direction central portion, and elongated oblique resilient and elastic members are fixed in an extended state in a direction from the folded part to the side edges of the inner body below the folded part.