A controller continues, from an output start, a single outputting phase in which only first electric energy is supplied to an electrode, and transitions the single outputting phase to a simultaneous outputting phase in which the first electric energy and second electric energy are simultaneously output and treated target is denatured due to both of a high-frequency current and treatment energy generated in a functioning element. The controller sets a parameter relating to the treatment energy in the simultaneous outputting phase and a duration of the simultaneous outputting phase, based on an impedance at a certain time point in the single outputting phase and/or a variation with time of the impedance in the single outputting phase.
