A disposable diaper comprising a fastening tape, to having a tab part at one end of a tape substrate, a fixing part at the other end of the tape substrate, and an adjustment part between the tab part and the fixing part； an attachment is fixed to the tab part, the fastening tape is attached to a side end of the front or back part of the diaper main body at the fixing part, the adjustment part is folded and temporarily joined to the diaper main body and/or to the fastening tape at a joining part, and a length of the fastening tape between the attachment and the joining part nearest to the attachment is longer than a length between an outer edge of the diaper main body and the joining part nearest to the attachment. The length of the fastening tape is thus stepwise adjustable to a size of a wearer's waist, and hence the disposable diaper of one size can be worn by people of various body types.
