A high-frequency incision tool has a flexible sheath which is adapted to be inserted into the body cavity along with an endoscope. A suction port is formed at the distal end of the sheath. A wire is inserted into the sheath and a part of the wire is exposed from the sheath to form an incision section. The wire is pushed and pulled by an operating section which is provided at the proximal end of the sheath. A suction mouthpiece is formed at the operating section to communicate with the suction port through the inside passage of the sheath. A reinforcing wire is disposed in the distal end portion of the sheath to reinforce the portion.