A method for manufacturing a disposable underpants type diaper provided with aseparator for preventing stool from touching the skin. A bending body of a sheet piece(20) for forming a separator (20a) is fixed to the inner surface of the front portionor the rear portion in the inseam region (6) of a diaper basic body having the inseamregion (6), the front waist region (7) and the rear waist region (8). The bendingbody is obtained by bending the sheet piece (20) along the center line in the firstwidth direction thereby superimposing a first half body and a second half bodyforming the sheet piece (20) and then bonding the end edges (21, 22) in both halfbodies at the central portion in the width direction (X). In a state where the firstwidth direction center line is brought close to the second width direction centerline dividing the diaper basic body (10a) into two in the front and back direction,inner surfaces at the front portion or rear portion of the inseam region (6) aresuperimposed, the outer surface at the opposite side edges of the first half bodyand the inner surface of the inseam region (6) are joined and the portion betweenthe opposite side edges is separated from the inner surface. Subsequently, thediaper basic body (10a) is bent along the second width direction center line, theinner surface of the diaper basic body (10a) and the outer surface at the opposite sideedges of the second half body are bonded and the portion between the opposite sideedges is separated from the inner surface. Inner surfaces at the side edges (7a,8a) of the front and rear waist regions (7, 8) of the diaper basic body (10a) thusbent are bonded to form the shape of underpants type.
