A catheter (1) comprises flat plate-like reinforcing wires (361) having a predetermined width-to-thickness ratio, and an outer layer (35) of a thermoplastic resin. The width and thickness of the reinforcing wires and the outside diameter of the catheter are in predetermined ratios to achieve a catheter whose proximal portion (31) is relatively rigid and excellent in kink resistance notwithstanding a relatively large inside diameter and a relatively small material thickness.
