A treatment instrument of the present invention includes an elongated instrument body, a cylindrical member constituting the instrument body, a transducer 32 provided in inside of the cylindrical member for applying ultrasonic vibration to a fluid flowing into a liquid feed passage, a fluid atomizing port 24k provided at the distal side of the instrument body for injecting the liquid which was given the ultrasonic vibration by the transducer 32 and atomized to a living tissue from the distal end of the instrument body, and an electrode 24 provided at the distal side of the instrument body for discharging high-frequency electric energy along the liquid injected from the fluid atomizing port so as to coagulate the living tissue.
