In an energy treatment system, a processor temporally detects an electrical property value of an ultrasonic transducer, holds a temporary peak value of the electrical property value, detects an impedance value between the probe electrode and the jaw electrode, and compares the electrical property value and the temporary peak value to determine whether a predetermined condition is satisfied, and whether the impedance value exceeds a predetermined threshold. In response to determining that the electric property value satisfies the predetermined condition and the impedance value is larger than the predetermined threshold, the processor performs at least one of: (i) stopping and (ii) decreasing output from the first power supply, and notifying the determination result.