Problem to be solved: to provide a driller capable of easily enlarging and enlarging holes formed on the wall of the digestive tract or the like.The shaft 21 of the ditor 20 is provided with a tapered portion 24 whose outer diameter is smaller than the outer diameter of the base end, the tip end portion 25 formed on the tip end side of the tapered portion 24, and the base end portion 23 provided on the proximal end side of the tapered portion 24, or the base end portion of the tapered portion 24 without having the leading end portion The base portion 23 has a base end 23.If the shaft 21 has no tip portion and has a base end 23The pitch of the adjacent portions along the axis a of the spiral convex part 22 provided in the tapered partIt is smaller than the pitch of adjacent portions along the axis a of the spiral convex portion 22 provided at the base endWhen shaft 21 has base end 23 and tip 25The pitch of adjacent portions along the axis of the spiral convex 22 provided in the tapered portionIt is larger than the pitch of adjacent portions along the axis a of the spiral convex portion 22 provided at the tip portion 25 or the base end portion 23.消化管等の壁に形成された孔を容易に拡径することができるダイレータを提供する。 ダイレータ２０のシャフト２１は、先端の外径が基端の外径よりも小さいテーパ部２４と、テーパ部２４の先端側に設けられた先端部２５およびテーパ部２４の基端側に設けられた基端部２３と、または、前記先端部を有さずに、テーパ部２４の基端側に設けられた基端部２３とを有する。シャフト２１が先端部を有さず基端部２３を有する場合、テーパ部２４に設けられた螺旋状の凸部２２の軸Ａに沿って隣り合う部分のピッチは、基端部２３に設けられた螺旋状の凸部２２の軸Ａに沿って隣り合う部分のピッチよりも小さく、シャフト２１が基端部２３および先端部２５を有する場合、テーパ部２４に設けられた螺旋状の凸部２２の軸に沿って隣り合う部分のピッチは、先端部２５または基端部２３に設けられた螺旋状の凸部２２の軸Ａに沿って隣り合う部分のピッチよりも大きい。
