Provided is a dilator that can easily widen the diameter of a hole formed in a wall of a digestive tract or similar. A shaft 21 of a dilator 20 has a tapered section 24, the outer diameter of a distal end thereof having a smaller outer diameter than the outer diameter of a proximal end thereof, and either a distal end section 25 that is provided to the distal end side of the tapered section 24 and a proximal end section 23 that is provided to the proximal end side of the tapered section 24, or a proximal end section 23 that is provided to the proximal end side of the tapered section 24, without the distal end section. If the shaft 21 does not have a distal end section but has the proximal end section 23, the pitch of sections of a helical protrusion 22 that is provided to the tapered section 24, said sections neighboring along an axis A, is smaller than the pitch of sections of a helical protrusion 22 that is provided to the proximal end section 23, said sections neighboring along the axis A. If the shaft 21 has the proximal end section 23 and the distal end section 25, the pitch of sections of the helical protrusion 22 that is provided to the tapered section 24, said sections neighboring along the axis A, is greater than the pitch of sections of a helical protrusion 22 that is provided to the distal end section 25 or the proximal end section 23, said sections neighboring along the axis A.L'invention concerne un dilatateur qui peut facilement agrandir le diamètre d'un trou formé dans une paroi du tractus digestif ou similaire. Un arbre 21 d'un dilatateur 20 a une section effilée 24, le diamètre externe d'une extrémité distale de celle-ci a un diamètre externe plus petit que le diamètre externe d'une extrémité proximale de celle-ci, et soit une section d'extrémité distale 25 qui est disposée sur le côté d'extrémité distale de la section effilée 24 et une section d'extrémité proximale 23 qui est disposée sur le côté d'extrémité proximale de la section effilée 24, ou u
