A treatment system includes a power source for heat generation which outputs power for heat generation, a grasping member having a heating element which applies the power for heat generation as thermal energy to a living tissue, and a control section which performs constant temperature control on the power source for heat generation on the basis of temperature of the heating element, and controls the power source for heat generation so as to finish application of the thermal energy and complete treatment if the power for heat generation becomes not more than predetermined threshold power which is independent of a type of the living tissue or if a rate of decrease in the power for heat generation becomes not more than a predetermined threshold rate.