To facilitate a continuous tight fit of a diaper to a wearer, a disposable diaper having one waist opening and a pair of leg openings is provided with: a front-side section; a back-side section; a crotch section; and a pair of extensible or stretchable leg sheets. Longitudinal peripheral edge regions and inner lateral edge regions of the leg sheets are respectively joined, on one side of the crotch section, to lower edge regions of the front-side section and back-side section and lateral edge regions of the crotch section. The leg sheets each have notches facing inward from the outer lateral edges thereof. The pair of leg openings are defined by joining outer lateral edge regions of the leg sheets adjacent to front-side starting ends of the notches, and outer lateral edge regions of the leg sheets adjacent to back-side starting ends of the notches.