A high-frequency treatment instrument 1 comprises a flexible tube 3 which is inserted into a body cavity and a treatment portion 2 which is located on the distal end of the flexible tube 3 where a high-frequency current is applied. In this high frequency treatment instrument 1, the flexible tube 3 is formed by a plurality of wound conductive wires and is provided with a multiple-thread coil 6 connected electrically to the treatment portion 2, and the high-frequency current is applied to the multiple-thread coil 6.
