To provide a disposable diaper which surely prevents the leakage from the sides by providing an absorbent layer which is excellent in diffusivity of excrement in the longitudinal direction, curves along the groin easily and shows excellent fitting performance.

The disposable diaper 10 is equipped with the absorbent layer 31 made by forming flocculent pulp into a layer between a liquid permeable surface sheet 11 and a liquid impermeable reverse sheet 21 and a front body 3 and a back body 5 on the front and back sides in the longitudinal direction of the absorbent layer 31. Grooves 32a and 32b extending along the longitudinal direction are formed on the front surface 31a and the back side 31b of the absorbent layer 31. Preferably, the groove 32a on the front surface 31a and the groove 32b on the reverse side 31b are formed alternately in the width direction of the absorbent layer 31.