A living tissue to be treated is brought into contact with a first high-frequency electrode having high thermal conductivity. A substrate on which an electric resistance pattern is formed is longer than the first electrode. The substrate includes an end portion projected from the first high-frequency electrode. A first lead connection portion electrically connected to the electric resistance pattern is formed on the projected end portion. The substrate is pasted to the first electrode by use of a high-thermal-conductivity heat-resistant adhesive sheet. A lead line for applying power to the electric resistance pattern is arranged in the first lead connection portion where it extends in the longitudinal direction of the first electrode and on the side close to the first electrode.
