A disposable diaper which can be used both as a tape-fastening type and an underpants type by joining the both side portions of the front body part and back body part respectively to thereby form joined portions on both sides along with a waist opening and a pair of right and left leg openings and in this diaper, perforated lines are formed on the both side portions of the front body part so as to extend from an edge of the waist opening to edges of the leg openings and at least one pair of fastening tapes having hook members on inner surfaces thereof and straddle the perforated lines.