Dilator

A dilator comprising:

• a hollow shaft comprising a tapered section having a diameter increasing from a distal end toward a proximal end of the hollow shaft;
• and
• a spirally-arranged protruding portion provided on an outer peripheral surface of the hollow shaft, the spirally-arranged protruding portion comprising (i) spirally-arranged protruding sections, and (ii) gaps between adjacent spirally-arranged protruding sections along an axial direction of the hollow shaft,
• wherein the spirally-arranged protruding portion includes:
• (i) an apex section having a greatest height from the outer peripheral surface in a transverse cross-section of the spirally-arranged protruding portion, and
• (ii) a side surface section facing outward and extending from the apex section toward the outer peripheral surface, the side surface section including an inclined surface inclined substantially linearly toward at least one of a distal end direction and a proximal end direction between the outer peripheral surface and the apex section in the transverse cross-section of the spirally-arranged protruding portion, and
• the spirally-arranged protruding portion comprises a coil body formed by winding a wire around the outer peripheral surface of the hollow shaft.