A tubular medical treatment instrument indwelling device for indwelling a stent graft expandable in the radial direction, includes a tubular sheath, a rod member configured to move forward and backward inside the sheath along the axial direction of the sheath, and a front tip provided in the forward end portion of the rod member and includes, formed therein, an engaging portion being engageable with an engagement portion provided in the stent graft. The engaging portion is formed in a position where it is hided inside the sheath when the forward end portion of the sheath is sealed with the front tip. The tubular medical treatment instrument indwelling device is capable of inhibiting damaging of a blood vessel or freeing of parietal thrombus/parietal atheroma from occurring.