One embodiment of this disposable diaper (1) is provided with an outer cladding (3) forming the outer surface thereof, and both side edges (A1, A1) of the outer cladding (3) at the body front area (F) are joined to both side edges (B1, B1) of the outer cladding (3) at the body rear area (R), thus forming a pair of side seals (4, 4), a waist opening (8), and a pair of leg openings (9, 9). The side seals (4) are formed by the side edges (A1) of the outer cladding (3) at the body front area (F) and the side edges (B1) at the outer cladding (3) at the body rear area (R) being joined at a fusion section (seal edge) (40) having the form of a continuous line extending the vertical direction (X). The side seals (4) at a partial region of the region extending from the waist opening (8) to the leg openings (9) are formed in a bumpy shape such that in a front view of the diaper (1), convexities outward in the widthwise direction and concavities inward in the widthwise direction are arranged in alteration are arranged in alternation in the vertical direction.