A treatment system includes an energy source apparatus having a high frequency power supply and a heater power supply. An elongated treatment tool is configured to be attached to the energy source apparatus to receive electrical energy. The elongated treatment tool includes a main body, a shaft, and a treatment portion all of which are attached to one another and are disposed on a longitudinal axis thereof. The treatment portion is used to grip a treatment target so as to apply appropriate gripping pressure to a point where the treatment target is to coagulate and to form a sealed region therein from an initial stage to a terminal stage of the treatment.
