A tape-type disposable diaper, comprising: a ventral part extending forward from the center in a front-back direction; a dorsal part extending backward from the center in the front-back direction; a crotch portion in which both side edges extend from the middle in the front-back direction of the ventral part to the middle in the front-back direction of the dorsal part; an absorber incorporated in a range including the crotch portion; wing parts extending outward in the width direction compared with the crotch portion in the ventral part and the dorsal part; and on both sides of the dorsal part, a connecting tape for detachably connecting the ventral part, wherein the lower edges of the wing part of the ventral part each extend so as to be located obliquely outward toward the front, the lower edges of the wing part of the dorsal part each extend so as to be located obliquely outward toward the back side, the lower edges (70, 75) of the wing parts in at least one of the ventral part and dorsal part have wavy portions having a plurality of peaks bulging outward, a side flap portion not including an absorber is provided on both sides in the width direction from the ventral part to the dorsal part, a side elastic member is provided on the center side in the width direction from the wing parts in the side flap portion, a flat gather contracted in the front-back direction by the side elastic member is provided, an overlapping range overlapping a front-back direction range in which contraction force of the side elastic member acts and at least a part of a front-back direction range of the wavy portion is provided, the maximum elongation of the flat gather is 150-350%, in the overlapping range, the width direction interval between the side elastic member and the wavy portion is at most 15 to 50 mm and at least 5 to 20 mm, characterized in that in the wavy portion, the total amplitude is gradually or continuously increased as approaching the crotch portion side. a ventral part extending forward from the center in a front-back direction; a dorsal part extending backward from the center in the front-back direction; a crotch portion in which both side edges extend from the middle in the front-back direction of the ventral part to the middle in the front-back direction of the dorsal part; an absorber incorporated in a range including the crotch portion; wing parts extending outward in the width direction compared with the crotch portion in the ventral part and the dorsal part; and on both sides of the dorsal part, a connecting tape for detachably connecting the ventral part, wherein the lower edges of the wing part of the ventral part each extend so as to be located obliquely outward toward the front, the lower edges of the wing part of the dorsal part each extend so as to be located obliquely outward toward the back side, the lower edges (70, 75) of the wing parts in at least one of the ventral part and dorsal part have wavy portions having a plurality of peaks bulging outward, a side flap portion not including an absorber is provided on both sides in the width direction from the ventral part to the dorsal part, a side elastic member is provided on the center side in the width direction from the wing parts in the side flap portion, a flat gather contracted in the front-back direction by the side elastic member is provided, an overlapping range overlapping a front-back direction range in which contraction force of the side elastic member acts and at least a part of a front-back direction range of the wavy portion is provided, the maximum elongation of the flat gather is 150-350%, in the overlapping range, the width direction interval between the side elastic member and the wavy portion is at most 15 to 50 mm and at least 5 to 20 mm,