PURPOSE: To prevent bending of a sheath to be retained in a blood vessel for introducing a catheter or a stent to a target position without-thickening.

CONSTITUTION: A reinforcement 2 spirally wound by fine metal wire is embedded in a sheath 1 excluding the front end and is given such a mechanical strength as to be retained without bending at sharply curved portions, nor exposing fine metal wire, so as to not to damage the vascular wall.