PROBLEM TO BE SOLVED: To provide a dilator, when being inserted into a body wall, being little affected by a boundary between a diameter-enlarged part and a body part.SOLUTION: A dilator 100 includes: a diameter-enlarged part 10 that has an insertion hole 110 in which a puncture needle 31 is inserted, and a portion 11, the diameter of which is enlarged as it separates from an opening p at a tip end of the insertion hole 110； and a shaft body 50 to which the diameter-enlarged part 11 is fitted and that is long along an opening direction of the insertion hole 110. Then, a boundary part between the diameter-enlarged part 10 and the shaft part 50 has a boundary line that includes at least one line segment traversing a virtual plate 513, with an axial center X of the shaft body 50 defined as a normal line.SELECTED DRAWING: Figure 1【課題】体壁への押入時に拡径部と胴体部との境界の影響がより少ないダイレータを提供する。【解決手段】穿刺針３１が挿入される挿入孔１１０を有し、挿入孔１１０の先端の開口部ｐから遠ざかるにしたがって径が大きくなる部位１１を有する拡径部１０と、拡径部１１が取り付けられて、挿入孔１１０の開口方向に沿って長い軸体５０と、を備えたダイレータ１００を構成する。このとき、拡径部１０と軸体５０との境界部分は、軸体５０の軸心Ｘを法線とする仮想平面５１３を横切る少なくとも１つの線分を含む境界線を有する。【選択図】図１
