This disposable diaper (1) for low-body-weight infant is provided with an absorbent core (2) having a narrow part in the central part in the longitudinal direction. With the diaper (1), which is folded in two, unfolded and stretched in the longitudinal direction, after being pressed against the upper surface of a base with the skin-facing surface facing downwards, and a plate and weight placed thereupon, achieving a natural state, the absorbent core (2) has a first region (S1) which follows the upper surface and a second region (S2) which is separated upwards from the upper surface, and a separate folding line (FLa) which forms the boundary between the first region (S1) and the second region (S2) is formed.一種具備在長邊方向的中央部具有狹窄部的吸收性芯(2)的低體重兒用的用後即棄式紙尿布(1)，將被對折的紙尿布(1)朝長邊方向展開且伸長的狀態下，將肌膚側面朝下按壓在台的上面後，將板子及砝碼放上之後，當成為自然狀態時，吸收性芯(2)具有：沿著上面的第1區域(S1)、以及從上面朝上方遠離的第2區域(S2)，並形成有成為第1區域(S1)與第2區域(S2)的邊界的其他的折線(FLa)。
