A disposable diaper has front and rear waist regions, a crotch region, and an absorbent chassis. The absorbent chassis includes an absorbent structure and a pair of side flaps. Each of the side flaps has layered sheet materials and includes a distal edge, a cuff branch line between the side edge of the absorbent structure and the distal edge, a leg-opening elasticized area between the cuff branch line and the distal edge, and a leakage-barrier cuff branched from the cuff branch line and intersecting with the leg-opening elasticized area. The leakage-barrier cuff has a free edge parallelly-spaced from the cuff branch line. The distance from the cuff branch line to the distal edge is larger than from the cuff branch line to the free edge. The number of sheet material layers included in the leg-opening elasticized area is larger than in the leakage-barrier cuff.
