The present invention is an unfolding disposable diaper, wherein: a main diaper body having mutually orthogonal longitudinal direction, transverse direction and thickness direction has a first waist-encircling section, a crotch section, and a second waist-encircling section lined up in the longitudinal direction； and a single waist-encircling opening and a pair of leg-encircling openings are formed by hooking fastening tapes, which protrude outward in the transverse direction from the second waist-encircling section, on the first waist-encircling section to connect the first waist-encircling section to the second waist-encircling section. The fastening tapes have: a base sheet that is fixed to the second waist-encircling section via a fixing part； and a hooking section that is provided on the base sheet at a position to the outside of the fixing part in the transverse direction and is able to hook on the first waist-encircling section. At least a portion of the base sheet between the fixing part and the hooking section is stretchable in the transverse direction. A cutting line for detaching the hooking section from the fixing part is formed on a portion of the base sheet between the fixing part and the hooking section.
