A high-frequency generator (100) for an electric surgical instrument includes a power supply (104) that generates a power, and a resonant circuit that excites a high-frequency signal. The resonant circuit includes a parallel resonant circuit (106) which is connected to the power supply (104), and a series resonant circuit (110) which is coupled to the parallel resonant circuit (106) and is connected to the electric surgical instrument (200). The parallel resonant circuit (106) has a higher parallel resonant frequency than a series resonant frequency of the series resonant circuit (110). Therefore, efficiency when a load (Z) as a living tissue treated by the electric surgical instrument (200) is high can be improved. In addition, stability when the load (Z) is high can be improved.
