In a resectscope apparatus of the present invention, by using an output from a second output transformer 131, high frequency current passes through a treating electrode 41 when the treating electrode 41 is in contact with a living tissue 152 in a conductive liquid 151. Then, the high frequency current flows between the treating electrode 41 and a return electrode 45. Thus, the treating electrode 41 generates heat. Bubbles 153 are formed from the conductive liquid 151 on the peripheral surface of the treating electrode 41 and cover the treating electrode 41. Interlelectrode resistance increases from a resistance R1 and becomes higher resistance to a substantially insulating state. Then, the voltage increases, and discharging occurs between the treating electrode 41 and the living tissue 152. By using the high frequency current from the discharging, the living tissue is treated.
