A resectoscope for endoscopic surgery with a tubular shaft and a handle, the shaft comprising a longitudinally displaceable electrode instrument and, at its distal end, an electrically insulating insert, the electrode instrument having an elongated shaft section with one or two support arms and, in its distal end region, an electrode that can be acted upon by high-frequency current, characterized in that the insulating insert has one or more guide elements for holding a support arm, the support arm being longitudinally displaceable in the guide element.