An energy output section outputs first electric energy so that a high-frequency current flows between electrodes through a treated target, and outputs second electric energy so that heat occurs in an end effector. A controller outputs the first electric energy at the same time as the second electric energy in at least a part of a period during which the heat is continuously denaturing the treated target from an output start of the second electric energy. The controller makes, based on judging that the treated target entered a predetermined state, an electric power of the first electric energy increased.
