Provided is an underwear-type diaper that fits the shape of an infant under half a year old and that is such that gather marks are not easily imparted. The underwear-type diaper (10) is provided with: a front waist region (18) and back waist region (19) that have a horizontal direction (X) and a vertical direction (Y) that are perpendicular to each other a crotch region (13) joined to the front and back waist regions and a leg cuff (40) that extends along both edges of the crotch region (13). Each of a front and a back waist panel is segmented into a first extending/contracting region (26) and a second extending/contracting region (27), the ratio of the dimensions in the vertical direction of the first extending/contracting region and the second extending/contracting region is in the range of 1:1.6-2.2, the elongation rate of the waist elastic body (30) attached to the first extending/contracting region is lower than the elongation rate of the waist elastic body attached to the second extending/contracting region, and the elongation rate of the waist elastic body attached to the second extending/contracting region is lower than the elongation rate of a second leg elastic body (42).Linvention fournit une couche de type culotte convenant à la forme du corps dun nourrisson de seulement quelques mois, et peu susceptible de laisser des marques de couture. Cette couche de type culotte (10) est équipée : dune région taille avant (18) ainsi que dune région taille arrière (19) possédant une direction largeur (x) et une direction longueur (Y) perpendiculaires lune par rapport à lautre dune région fourche (13) raccordant les régions taille avant et arrière et de revers de jambe (40) se prolongeant suivant les deux bords latéraux de la région fourche (13). Des panneaux de taille avant/arrière sont divisés chacun en première région extension/contraction (26) et en seconde région extension/contraction (27). Le rapport de dimension dans la direction longueur de la première régio
