One surface of a belt-shaped sheet laminate (10) (continuous diaper strip), in which a plurality of sheets are laminated, is made to abut against a support member (21) having a light passage section (27) through which a laser beam (30) can pass, and the belt-shaped sheet laminate (10) which is in a pressurized state is irradiated, from the support member (21) side via the light passage section (27), with a laser beam (30) having a wavelength that is absorbed by the sheets constituting the sheet laminate (10) and that causes the sheets to generate heat, and thus, the belt-shaped sheet laminate (10) is cut and separated and, simultaneously, cut edge sections created, by the cutting/separation, in the plurality of sheets which are in the pressurized state are fusion-bonded together. Thus, sealed edge sections (4) (side seal sections) are formed by fusion-bonding the edge sections of the plurality of sheets in a state where the sheets' edge sections are superposed.
