The present invention provides a high-frequency treatment apparatus including: an electrode assembly electrically connected to a high-frequency generating unit for generating a high-frequency current, the assembly having, at the distal end thereof, a current-applying electrode for discharging the high-frequency current, the proximal end of the current-applying electrode being covered with an insulator; an insertion section receiving the electrode assembly, the insertion section being located on the return side of the high-frequency current discharged from the current-applying electrode; a liquid supply section for supplying an irrigation liquid to the vicinity of the current-applying electrode; and an opening section provided at the distal end part of the insulator, the opening section supplying a gas to the vicinity of the current-applying electrode.