The high-frequency treatment instrument is a high-frequency treatment instrument for performing a high-frequency treatment on a pathological lesion portion (subject tissue) not shown and includes a sheath (elongated extension member), a treatment electrode which is rotatably disposed at a distal end of the sheath and which extends in a direction substantially parallel to a diameter direction of the rotation, an operating wire (axial member) for allowing the treatment electrode to rotate around the distal end of the sheath, and an operating portion to which proximal ends of the sheath and the operating wire are connected. According to a high-frequency treatment instrument, by enabling a treatment on a subject tissue without using a curving operation of an endoscope it is possible to facilitate a procedure.
