Method for manufacturing a disposable diaper of the open type with a main part (4) comprising a front section (6) with front side longitudinal edges (42), a back section (8) with rear side longitudinal edges (41) and a section of gland (10) that is arranged between the two previous sections in the longitudinal direction (28) and is placed between the legs of a user, the main part (4) comprising an absorption body (12), and with rear side sections (20) connected on both sides to the dorsal section (8) and front side sections (22) connected on both sides to the front section (6), which extend in the transverse direction (30) beyond of the front and rear lateral longitudinal edges (42, 41) of the main part (4) and join the front section (6) and the dorsal section (8) with each other in the placed state of the disposable incontinence diaper le, where, to form cut-off leg areas, the lateral sections (20, 22) are configured at least on the edges (17) turned towards the section of the groove (10) so that they run obliquely with respect to the longitudinal direction (28) or have a curved shape, and the main part (4) is configured in the form of an hourglass at least in the slit section, the procedure of which comprises the following steps: feeding of a band of endless flat material (50 , 50a) in a longitudinal direction (28) for manufacturing sections of material (66, 66a) intended for the formation of side sections (20, 22), formation of first recesses (52) in the material along a first cutting line (100) on a side edge (70, 70a, 70b) of the flat material band (50, 50a) to generate contoured cuts in the flat material band (50, 50a), where a parallel imaginary PL to the longitudinal direction, which is ap located at point P of the maximum extension of the cut in the transverse direction to the longitudinal direction (28), it defines an outer partial zone (80) and an inner partial zone (81) of the flat material band (50), folded from the band of flat material (50, 50a) aroun
