A treatment system 10 includes a high-frequency power source 73 which outputs high-frequency power, a power source 83 for heat generation which outputs power for heat generation, one pair of jaws 36a, 36b having one pair of electric conductors 52a, 52b which are disposed at respective grasping surfaces and a heater member 53 which is disposed at at least one of the jaws, and a control section 94 which performs control to start application of the thermal energy after application of the high-frequency power energy ends, repeats a first control mode of performing control such that the heater member 53 reaches a first temperature and a second control mode of performing control such that a temperature of the heater member 53 becomes lower than the first temperature, and controls the power source 83 for heat generation according to a temperature change parameter based on change in temperature of the heater member 53 so as to end application of the thermal energy.
