A dilator includes a hollow shaft having a tapered portion and a body portion having a distal end located at a proximal end of the tapered portion. The tapered portion has an outer diameter that is smaller at a distal end than at a proximal end, and the body portion extends toward a proximal end side in an axis direction of the shaft. A spirally-arranged protruding portion is provided on an outer peripheral surface of the tapered portion, and the spirally-arranged protruding portion has gaps between adjacent portions of the spirally-arranged protruding portion along an axis direction of the shaft. A proximal end of the spirally-arranged protruding portion is located at the proximal end of the tapered portion.
