Microwave-irradiating surgical instruments for endoscopic forceps or scope-assisted surgery forceps that have long lead wires often generate heat even during microwave transmission and a water supply device for cooling is necessary. Accordingly, conventional surgical instruments that irradiated energy such as microwaves had a separate passage for passing water (a water supply device) inside the forceps or endoscope. Due to the space occupied by said water supply device, the image cable or work hole diameter could not be enlarged. Moreover, the presence of the water supply device made surgery difficult. The present invention was completed by the discovery that a microwave-irradiating instrument wherein the central conductor is hollow and forms a channel and said channel is used as a water supply tube, etc. solves the above problems without affecting microwave irradiation efficiency.