In the present invention, a thread is cut in a manner such that the end of a ligation loop after cutting does not later obstruct a region of observation or a region of treatment. Provided is a treatment tool (1) that is for atrial appendage ligation and that is provided with: a shaft (2) to which is provided a lumen (4) having at the tip an opening (4a) having an opening diameter such that a knot (6) cannot pass through and a thread (5a) of a ligation loop (5) formed in a tightenable loop shape can pass by means of one end of the thread (5a) being connected to an intermediate position by means of the knot (6); and a cutting section (3) that is provided to the tip of the shaft (2) and that cuts the thread (5a) passing through the lumen (4) at the inside of the opening (4a) at the vicinity of the opening (4a).
