A high-frequency incision tool for endoscope comprises a sheath inserted through and extracted from a treatment tool guide lumen of an endoscope; an operation unit connected to the rear of the sheath; a pair of electrode blades disposed in parallel and oriented forward at the front position of the sheath, the pair of electrode blades opening forward and closing back through remote manipulation of the operation unit; and a planar portion provided at the tip of at least one of the electrode blades, the planar portion having a projected area, when viewed from the front, larger than the cross sectional areas of the electrode blades at a portion close to their front ends.