PROBLEM TO BE SOLVED: To provide a diaper for a low-weight infant, making a belt member hardly come off from a body part during wearing.SOLUTION: A diaper (1) for a low-weight infant comprises an absorber (21) having at least an absorbent core (21a), an exterior sheet (24) arranged at a non-skin side of the absorber (21), and a belt member (30). The belt member (30) has locking members (31A, 31B) at one side and the other side in the longitudinal direction of the belt member (30). In a state that the belt member (30) is locked by the locking member (31A) at the one side, to the inside of an outside end (24leo) of the exterior sheet (24) in the longitudinal direction, and to a non-skin side of the exterior sheet (24) in the thickness direction, an outside end (21leo) of the absorbent core (21a) is positioned in the inner side than an intermediate portion between the outside end (24leo) of the exterior sheet (24) and an outside end (31Aleo) of the locking member (31A) at the one side.SELECTED DRAWING: Figure 6COPYRIGHT: (C)2019,JPO&INPIT【課題】着用時にベルト部材が本体部から離脱し難い低体重児用のおむつを提供する。【解決手段】少なくとも吸収性コア（２１ａ）を備えた吸収体（２１）と、吸収体（２１）よりも非肌側に配された外装シート（２４）と、ベルト部材（３０）と、を有する低体重児用おむつ（１）であって、ベルト部材（３０）は、ベルト部材（３０）の長手方向の一方側及び他方側に係止部材（３１Ａ，３１Ｂ）を備えており、一方側の係止部材（３１Ａ）によって、ベルト部材（３０）が、長手方向における外装シート（２４）の外側端（２４ｌｅｏ）よりも内側、かつ、厚さ方向における外装シート（２４）の非肌側に係止された状態において、長手方向において、吸収性コア（２１ａ）の外側端（２１ｌｅｏ）は、外装シート（２４）の外側端（２４ｌｅｏ）と一方側の係止部材（３１Ａ）の外側端（３１Ａｌｅｏ）との中間よりも内側に位置している。【選択図】図６
