An underwear-type diaper, provided with: a diaper body (2) having a front section (20) for covering a wearers ventral side, a back section (21) for covering a wearers dorsal side, and a crotch section (22) between the front section (20) and the back section (21) one side panel (3) overlapping in a waist-encircling direction with one side edge of the front section (20) and with one side edge of the back section (21) and a different side panel (3) overlapping in the waist-encircling direction with a different side edge of the front section (20), separated in the waist-encircling direction from the one side edge thereof, and with a different side edge of the back section (21), separated in the waist-encircling direction from the one side edge thereof, wherein the side panels (3) are seamlessly continuous in the waist-encircling direction and contain a filamentous elastic member (F) extending in the waist-encircling direction and a pair of webbings (W) sandwiching the elastic member.
