An object of the present invention is to provide a dilator allowing the completion of hole expansion on a target object to be accurately detected.A dilator 1 includes a hollow shaft 11 having a tapered portion 111 and a body portion 112 having a front end located at a base end 111b of the tapered portion 111, the tapered portion 111 having an outer diameter of a front end smaller than that of the base end, the body portion 112 extending toward a base end side in an axis direction of the tapered portion 111, in which a spirally-arranged protruding portion 21 is provided on an outer peripheral surface 111A of the tapered portion 111, and the spirally-arranged protruding portion 21 has a gap 21a along an axis direction of the shaft 11, and a base end 21b of the spirally-arranged protruding portion 21 is located at the base end 111b of the tapered portion 111.
