A stent delivery system is provided with a stent which, when inserted into an organism, is compressed in the center axis direction and which, when placed in the organism, can be expanded outward and restored to the shape which the stent has before being compressed; an inner tube body (inner tube); and a stent housing tube body (sheath) in which the stent is housed. The stent can be discharged by moving the stent housing tube body to the proximal side relative to the inner tube body. At least a portion of an inner surface of the stent housing tube body is a substantially polygonal prism-shaped inner surface which extends in the axial direction of the stent housing tube body.