An ultrasonic-surgical and electrosurgical system includes an ultrasonic surgical device and an electrosurgical device which supply an ultrasonic signal and a high-frequency signal, respectively, to an ultrasonic/high-frequency treatment instrument capable of performing an ultrasonic treatment and a high-frequency treatment, and a relay device which is built in one of the devices including: a switch detection unit for detecting turn-on/off of a switch unit which performs on/off control of operations of the devices a switch element for outputting a switch signal which is used for on/off of outputs of the ultrasonic signal and the high-frequency signal to each of the devices in accordance with the detection output and a control unit for performing on/off control of the switch signal to control at least one of an output timing and an output mode of each of the signals.
