Present invention is a medical catheter apparatus used for implanting a vascular stent into a vessel of a living body comprising a catheter (2) provided with a balloon (3), on which a vascular stent (4) is mounted, and a sheath into which the catheter is relatively movably inserted. The catheter is provided at the middle portion with a guide wire leading-out opening (11) for leading out the inserted guide wire (9) toward the side direction of the catheter, the sheath is provided at a middle portion with a guide wire drawing-out opening (13) for drawing the guide wire drawn from the catheter out of the sheath, and a guide wire drawing-out guiding mechanism (14) is provided between the guide wire leading-out opening and the guide wire drawing-out opening for guiding the guide wire led out from the guide wire leading-out opening to the guide wire drawing-out opening. The guide wire drawing-out guiding mechanism has a variable length from the guide wire leading-out opening to the guide wire drawing-out opening which varies in accordance with the relative movement of the sheath with respect to the catheter.
