An open-type absorbent disposable incontinence diaper, includes a main part which includes an absorbent element, a front region having front lateral longitudinal edges, a rear region having rear lateral longitudinal edges, and a crotch region arranged between the front and rear regions. The diaper also includes rear side sections joined to the rear region on both sides and front side sections joined to the front region on both sides, said sections extending in the transverse direction beyond the lateral front and rear longitudinal edges of the main part. For forming rear side-section leg opening regions, a lower edge of a rear side section is curve-shaped. A ration of a length of the lower edge to a width of the lower edge is 0.40-0.90 and a ratio of a longitudinal extent of an extreme point of a convex portion of the lower edge to a transverse extent of the extreme point is 0.15-0.80.
