A surgical system includes a surgical instrument including a conducting section transmitting ultrasound vibration generated by an ultrasound transducer to a distal end portion and transmitting a high-frequency output signal to the distal end portion, an ultrasound drive section outputting an ultrasound drive signal to the ultrasound transducer, a high-frequency output section outputting a high-frequency output signal to the conducting section, a detection section detecting an ultrasound impedance of a surgical site to which ultrasound energy and high-frequency energy are provided from the distal end portion by outputting both signals simultaneously to the surgical instrument, a determination section determining whether the detected ultrasound impedance is in a predetermined range, and a control section performing control to increase a high-frequency output value by a first predetermined amount or decrease the high-frequency output value by a second predetermined amount when the detected ultrasound impedance is out of the predetermined range.