A treatment tool provided with: a rod shaped cutting section which is adapted to be endoscopically inserted into a body cavity and is for performing cutting procedures to a tissue inside a body cavity through a transmission of high frequency current; a wire, the cutting section connected at the distal end thereof; a sheath consisting of an insulating material, into which the wire is inserted; a main body, the back end of the sheath being connected thereto; a slider to which the back end of the wire is fixed and which is disposed to the main body to enable sliding in the axial direction; wherein the cutting section has a large diameter part at the distal end of the cutting section and wherein the treatment tool further comprises a tubular distal member which has a through hole along the axis and is attached to the distal end of the sheath, the diameter of the through hole being smaller than the outer diameter of the large diameter part so that, even if the cutting section is maximally retracted along the direction toward the back end of the sheath, it is impossible to house the large diameter part within the sheath, characterized in that the large diameter part has a semispherical part which is formed to be semispherical in shape and is provided on the distal end side of the cutting section, the semispherical part being directed toward the distal end side of the cutting section, and the tubular distal member includes a rounded tip which is exposed outside the sheath, wherein the outer distal surface of the rounded tip is formed to be curving, and to have a form which does not have angles or edges. a rod shaped cutting section which is adapted to be endoscopically inserted into a body cavity and is for performing cutting procedures to a tissue inside a body cavity through a transmission of high frequency current; a wire, the cutting section connected at the distal end thereof; a sheath consisting of an insulating material, into which the wire is inserted; a main body, the back end of the sheath being connected thereto; a slider to which the back end of the wire is fixed and which is disposed to the main body to enable sliding in the axial direction; wherein the cutting section has a large diameter part at the distal end of the cutting section and wherein the treatment tool further comprises a tubular distal member which has a through hole along the axis and is attached to the distal end of the sheath, the diameter of the through hole being smaller than the outer diameter of the large diameter part so that, even if the cutting section is maximally retracted along the direction toward the back end of the sheath, it is impossible to house the large diameter part within the sheath, characterized in that the large diameter part has a semispherical part which is formed to be semispherical in shape and is provided on the distal end side of the cutting section, the semispherical part being directed toward the distal end side of the cutting section, and the tubular distal member includes a rounded tip which is exposed outside the sheath, wherein the outer distal surface of the rounded tip is formed to be curving, and to have a form which does not have angles or edges.