To improve the ventilation properties of a sheet used in a flute structure. This disposable diaper has formed therein, on at least one of a front part and a rear part, a cushion part (40). In the cushion part (40), in a state where a waist expansion member (43) is stretched in the width direction of the diaper, the member is sandwiched and secured between an inner sheet (41) and an outer sheet (42). In the cushion part (40), a cushion forming sheet (44) overlaps one or both of the inner sheet (41) and the outer sheet (42), and is intermittently joined thereto so that in the width direction joining portions (51) and nonjoining portions (52) are alternatingly continuous. Formed in the cushion forming sheet (44) are a plurality of openings (60) or depressions that are grouped into row groups (R) and column groups (C). A continuous line (A) links the plurality of openings (60) or depressions which belong to the column group (C), and the line is inclined at a prescribed angle (θ) with respect to a reference line (F) that extends in the longitudinal direction.
