An endoscopic surgical instrument comprising: an insertion section configured to be inserted into a body cavity and comprising a tip end part, a base end part, and a central axis extending from the tip end part to the base end part in a longitudinal direction of the insertion section; a vein keeper arranged at the tip end part of the insertion section and configured to hold a blood vessel to be harvested; a surgical section arranged at the tip end part of the insertion section at a position shifted from the central axis in a radial direction of the insertion section and configured to cut off a side branch from between the blood vessel to be harvested and a wall portion in the body cavity; a first electrode disposed on a first surface of the surgical section that faces the vein keeper side; and a second electrode disposed on a second surface of the surgical section, the second surface being an opposite surface to that of the first surface, wherein the vein keeper comprises a holding base configured to hold a blood vessel to be harvested, and an axis connected to the holding base and extending through the insertion section, wherein the axis is movable backward and forward in the longitudinal direction of the insertion section to move the holding base disposed in front of the tip end forward and backward; and wherein the surgical section comprises a body section disposed within a notched part which is formed in the upper surface of the insertion section, is movable in the longitudinal direction of the insertion section; and characterized by a third electrode disposed on the second surface of the surgical section; a switching section configured to switch to one of an incision mode in which the side branch is cut off by supplying a current to the first electrode and the second electrode from an electric energy supply source and a coagulation mode in which the wall portion in the body cavity is coagulated by supplying a current to the second electrode and the third electrode from the electric energy supply source, and wherein the surgical section further comprises a V-shaped groove which is formed in a tip end of the surgical section and serves as a guiding section which guides an object to the first electrode when the surgical section moves toward the object. an insertion section configured to be inserted into a body cavity and comprising a tip end part, a base end part, and a central axis extending from the tip end part to the base end part in a longitudinal direction of the insertion section; a vein keeper arranged at the tip end part of the insertion section and configured to hold a blood vessel to be harvested; a surgical section arranged at the tip end part of the insertion section at a position shifted from the central axis in a radial direction of the insertion section and configured to cut off a side branch from between the blood vessel to be harvested and a wall portion in the body cavity; a first electrode disposed on a first surface of the surgical section that faces the vein keeper side; and a second electrode disposed on a second surface of the surgical section, the second surface being an opposite surface to that of the first surface, wherein the vein keeper comprises a holding base configured to hold a blood vessel to be harvested, and an axis connected to the holding base and extending through the insertion section, wherein the axis is movable backward and forward in the longitudinal direction of the insertion section to move the holding base disposed in front of the tip end forward and backward; and wherein the surgical section comprises a body section disposed within a notched part which is formed in the upper surface of the insertion section, is movable in the longitudinal direction of the insertion section; and a third electrode disposed on the second surface of the surgical section; a switching section configured to switch to one of an incision mode in which the side branch is cut off by supplying a current to the first electrode and the second electrode from an electric energy supply source and a coagulation mode in which the wall portion in the body cavity is coagulated by supplying a current to the second electrode and the third electrode from the electric energy supply source, and wherein the surgical section further comprises a V-shaped groove which is formed in a tip end of the surgical section and serves as a guiding section which guides an object to the first electrode when the surgical section moves toward the object.