A treatment system includes a high-frequency power source, a heat generation power source, a grasping member having an electric conductor which applies high-frequency power energy to a living tissue and a heating element which applies thermal energy, a memory where a predetermined impedance value or a predetermined rate of increase in impedance that is a threshold value, at which application of the high-frequency power energy is ended, is stored in advance, a first control section which controls the high-frequency power source based on the threshold value to end application of the high-frequency power energy, and a second control section which performs constant temperature control on the heat generation power source such that the heating element reaches a setting temperature that is set to be higher than a temperature of the heating element calculated from a resistance value of the heating element when application of the high-frequency power energy ends.
