A treatment device is provided including a catheter having a lumen that is opened to a distal end of the catheter a wire passing through the lumen so that the wire is inserted into or retracted from the lumen and a piece disposed at a distal end of the wire and having the maximum width when the piece is protruded from the distal end of the catheter is set larger than the diameter of the lumen, wherein the piece body 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 piece being extended in the axial direction by the lumen and reduced in its outer diameter so as to be pulled into the lumen.
