There is disclosed a stent delivery system includes a first cylindrical member capable of being inserted into a forceps channel of an endoscope and including a through hole having a central axis; a second cylindrical member inserted into the through hole of the first cylindrical member and capable of advancing/retreating with respect to the first cylindrical member, the second cylindrical member including a holding mechanism which holds a relative position of the second cylindrical member with respect to the forceps channel of the endoscope, and a stent which is attached between the first and second cylindrical members in a state where a diameter of the stent is reduced by the first cylindrical member and which expands when the first cylindrical member is removed.