PROBLEM TO BE SOLVED: To provide a disposable diaper wherein planar gathers are easily opened when wearing and can be properly fitted around legs.SOLUTION: In this disposable diaper, a gather sheet 62 and a liquid-impermeable sheet 11 of each side flap part SF are joined at least in a side end part 91, a strip-like non-junction area 90 wherein the gather sheet 62 and the liquid-impermeable sheet 11 are not joined is extended along the longitudinal direction on the more central side in the width direction rather than the side end part 91, and each side flap part SF is provided with side edge part elastic expansion/contraction members 81 extending in the longitudinal direction through the middle in the width direction of the non-junction area 90. In the non-junction area 90, the side edge part elastic expansion/contraction members 81 are fixed to the gather sheet 62 in a state that the side edge part elastic expansion/contraction members 81 are stretched in the longitudinal direction, and are not fixed to the liquid-impermeable sheet 11.
