A puncture instrument capable of punctured high frequency treatments. The puncture instrument essentially includes: a guide tube to be inserted into an intracavitary portion of a patient; a puncture needle member having an elongated needle body slidably received in the guide tube, and a sharp-pointed needle head provided contiguously at the fore end of the elongated needle body and protrudable out of the guide tube to penetrate into a target intracorporeal portion to be treated when the needle body is manipulated in a forward direction; and a high frequency electrode provided on a fore end portion of the needle body to be penetrated into the target intracorporeal portion together with the sharp-pointed needle head.