A dilator includes a first section, a second section, a third section, and a fourth section which have different diameters and are adjacent to each other in an axial direction, an angle formed by an outer peripheral surface of the first section with respect to the axial direction is smaller than an angle formed by an outer peripheral surface of the second section with respect to the axial direction, the angle formed by the outer peripheral surface of the second section with respect to the axial direction is larger than an angle formed by an outer peripheral surface of the third section with respect to the axial direction, and the angle formed by an outer peripheral surface of the third section with respect to the axial direction is smaller than an angle formed by an outer peripheral surface of the fourth section with respect to the axial direction.
