A disposable diaper includes a main body and a supplemental member, the main body being formed on its inner surface in its transversely middle zone with a cavity adapted to receive excretion, for example, feces. The cavity is defined by a pair of side walls spaced apart from each other by a predetermined distance in the transversely middle zone of the main body and extending longitudinally of the main body, and a top wall extending between distal edges of the respective side walls. The top wall is formed with openings adapted to guide feces and urine, respectively, and elastic members are secured to the supplemental member in the proximity of upper edges of the respective side walls so as to be operatively associated with a crotch region of the diaper.