An electrode for an electrosurgical unit is used for ablating and necrosing a living tissue by RF electric energy. The electrode can be a hollow electrode formed in an elongated hollow tube shape, including a non-insulating region of a predetermined length formed on one side, and an insulating region formed on an outer surface other than the non-insulating region. The electrode further can include a saline solution circulation structure that supplies pressurized saline solution for cooling a living tissue which is in contact with the hollow electrode from the outside of the living tissue to the inside of the hollow electrode, and one or more saline solution discharge holes formed in the non-insulating region of the hollow electrode to discharge some of the circulating pressurized saline solution to the living tissue.