Provided is a dilator capable of easily including the diameter of a hole formed in the wall of the digestive tract and the like. A dilator 30 includes a hollow shaft 31 having an outer diameter of a front end smaller than that of a base end, and a connector 9 connected to the base end of the shaft 31. A spirally-arranged protruding portion 32 protruding outwardly is provided on an outer peripheral surface 31B of the shaft 31. The spirally-arranged protruding portion 32 has gaps between adjacent portions along an axis A of the shaft 31. The shaft 31 has a first position P5 and a second position P6 along the axis, the second position P6 being located at a front end side relative to the first position P5 and having an outer diameter smaller than that of the first position P5. Inclination angles of the spirally-arranged protruding portion 32 to the axis A at the second position P6 is configured to be smaller than that at the first position P5.
