A high-frequency generator for high-frequency surgery is driven by a d.c. voltage supply. This d.c. voltage supply has a first working mode for transferring energy in a direction of the high-frequency generator, and also a second working mode for transferring energy in an opposite direction. With this arrangement, a particularly fast and efficient regulation of output voltage of the generator is possible. Therefore a reliable first cut may be performed on different kinds of tissue without any coagulation. Furthermore, owing to a high efficiency, a particularly small constructional size can be achieved.