A treatment device (1, 41, 51, 61, 71, 81, 111) is provided including a catheter (4, 84, 72) having a lumen (5) that is opened to a distal end surface (4A, 72A) of the catheter a wire (6) passing through the lumen so that the wire is inserted into or retracted from the lumen and a distal piece (10, 42, 52, 62) disposed at a distal end of the wire and having the maximum width when the distal piece is protruded from the distal end of the catheter is set larger than the diameter of the lumen, wherein the distal piece body (12, 43, 53, 64) is formed of a deformable material having a broad curved surface shape that distributes concentration of pressure acting on tissues, and when the wire is pulled in toward the catheter, the distal piece being extended in the axial direction by the lumen and reduced in its outer diameter so as to be pulled into the lumen.
