A disposable diaper (1) for a baby having a weight equal to or smaller than 3000 g, the disposable diaper includes: side flaps (14) a pair of fastening tapes (30) provided to the side flaps and a target region (29) that is engageable with the fastening tapes. One of the fastening tapes, of the pair of the fastening tapes, is engageable in an overlapping manner with another of the fastening tapes. In the case where an engaging force of the target region and the one of the fastening tapes is P1, and an engaging force of the one of the fastening tapes and the other of the fastening tapes is P2, a relation is P1 > P2 > 0.1 N/10 mm. In the case where the pair of the fastening tapes are overlapped in a state where centers of the fastening tapes in a tape width direction are matched, an upper side fastening tape is engageable to the target region, in both sides of the upper side fastening tape straddling over an end portion of a lower side fastening tape in the tape width direction.
