To provide a disposable diaper excellent in fit of the crotch section, prevention of leakage, and prevention of rewet. A disposable diaper 1 of the invention includes a top sheet 2 defining the skin facing side, an outer sheet 3 defining the non-skin facing side, and an absorbent member 4 between these sheets. The absorbent member 4 includes an absorbent core 40 oblong in the longitudinal direction X corresponding to the front-to-rear direction of a wearer. The absorbent core 40 contains an absorbent polymer. Upon defining an absorbent crotch region 40c in a narrowed portion of the absorbent core 40, the absorbent core 40 has a large area region 40a and a small area region 40b different in area from each other, one forward and the other rearward of the absorbent crotch region 40c. The absorbent core 40 has a slit 7 extending in the longitudinal direction from the absorbent crotch region 40c to the large area region 40a. The slit 7 intersects a transverse centerline CL of the outer sheet 3, with at least 80% of the total length of the slit 7 located in the side of the large area region 40a of the centerline CL. The width W2 of the slit 7 in the large area region is larger than the width W1 in the crotch region 40c.
