The invention relates to a high-frequency surgical device for generating high-frequency energy for cutting and/or coagulating biological tissue. The high-frequency surgical device comprises an application part being electrically connectable to an electrosurgical instrument having at least one activation switch, an intermediary power circuit galvanically separated from the application part, a DC power source which, in operation, provides in the application part at least one DC voltage, a with the DC voltage source electrically connected control signal generator which, in operation, generates in the application part (10) from the DC voltage an alternating control signal with a predetermined switching frequency, and a to the control signal generator electrically connected evaluation unit being electrically connectable to the activation switch of the instrument and which, when the activation switch is actuated, transmits a with the switching frequency oscillating activation signal to the input power circuit.