A surgical system includes: a treatment portion for treating living body tissue targeted for treatment； an ultrasound supplying section for supplying ultrasound via ultrasound transducers which produce ultrasound vibration； a radio-frequency electrical power supplying section for supplying, to the treatment portion, radio-frequency electrical power having an output wave-form defined by a base frequency and a repetition frequency； and a controlling section for controlling at least one of a voltage root-mean-square value and a crest factor, so that the voltage peak value of the output wave-form of the radio-frequency electrical power does not exceed a fixed value.
