An ultrasonic surgical system includes an ultrasonic transducer, a probe, and at least one circuit. The ultrasonic transducer is designed to ultrasonically vibrate. The probe is coupled to the ultrasonic transducer and is designed to treat a living tissue by the ultrasonic vibration. The circuit performs functions including detecting a pressing force of the probe against the living tissue, calculating a value of a product of the pressing force, an amplitude of the ultrasonic vibration, and a resonance frequency of the probe, comparing the calculated value with a predetermined product value, and generating a predetermined signal based on a result of the comparison.
