An atrial-appendage ligation treatment tool including: a shaft provided with a lumen having, at a distal end thereof, an opening having an opening diameter that allows passage of a thread of a ligation loop formed in a ring shape, which can be tightened, by connecting an end of the thread at an intermediate position by means of a knot and that does not allow passage of the knot； and a cutting part that is provided at a distal end of the shaft and that cuts, at an inner side of the opening and in the vicinity of the opening, the thread passing through the lumen.
