In a treatment instrument, a load force center of a load force, which is a sum of gravity acting on the treatment instrument and an external force caused by a connected cable, is positioned between two support members of a handle section, and a location of introduction of the cable is disposed in a manner to extend therebetween. In the treatment instrument, an ultrasonic vibration element unit is attached and rotatably coupled to a handle unit, a power receiving section or a power supply section at the coupling constitutes a rotary electrode structure by a cylindrical electrode and a terminal electrode, and power from an outside is received and transmitted between the handle unit and the ultrasonic vibration element unit.
