The invention provides a dilator having characteristics as an inexpensive instrument that allows insertion of a guidewire for assisting insertion of a catheter into a vessel in a simple and smooth manner. A first through-hole 5 into which a guidewire can be inserted is pierced over an entire region of a dilator 1 from a distal end face 3a to a rear end face 3b in the longitudinal direction of the dilator. A second through-hole 7 into which a guidewire can be inserted is pierced over a region of the dilator 1 from a midway to the rear end face 3b in the longitudinal direction of the dilator. A tapered portion 9 is formed such that it is tapered toward the distal end face 3a. An opening 7a a of the second through-hole 7 is open on the surface of the tapered portion 9.
