Present invention is a medical catheter apparatus used for implanting a vascular stent into a vessel of a living body comprising a catheter (2) including a distal portion where a balloon (3) attaching a vascular stent (4) is provided, and a sheath (1) into which the catheter is inserted and to be moved relative to the catheter between the section where it covers the balloon on which a vascular stent is mounted and the section where it exposes the vascular stent mounted on the balloon. The sheath comprises a first tubular member (15) covering the distal portion at which the balloon is provided, and a second tubular member (16) covering the proximal portion of the catheter and connected with the first tubular member. The first tubular member is formed of a tubular member capable of flexible deformation and the second tubular member is formed of a tubular member less extensible in the axial direction than the first tubular member.
