A disposable diaper to prevent an undesirable step from being formed due to downward displacement of a front end flap of an absorbent chassis during use of the diaper, to prevent body waste from leaking out and to assure a good appearance.A front waist region includes elasticized regions extending at least in the transverse direction Y, wherein the elasticized regions comprise a first elasticized region defined between a waist-opening peripheral edge and a front end flap of the absorbent chassis so as to extend in the transverse direction Y. A second elasticized region is defined adjacent the first elasticized region so as to extend in the transverse direction Y, and a pair of third elasticized regions are defined adjacent the second elasticized region and spaced from and opposed to in the transverse direction Y on both sides of a non-elasticized region formed in a transverse middle of the front waist region. The second elasticized region extends across the front flap of the absorbent chassis.