A catheter (1) comprises flat plate-like reinforcing wires having a predetermined width-to-thickness ratio, and an outer layer of a thermoplastic resin. The width and thickness of the reinforcing wires and the outside diameter (D1) of the catheter are in predetermined ratios to achieve a catheter whose proximal portion is relatively rigid and excellent in kink resistance notwithstanding a relatively large inside diameter and a relatively small material thickness.
