Abstract: This invention relates to an arrangement for driving a high-frequency oscillating tool arrangement (1) which includes, inter alia, a device (1a) whose form changes with a change in voltage, utilizing an electric drive circuit (2) constructed to generate alternating voltage which can be connected to the device and the frequency of which is adapted, through a first control circuit (7), to a value (C1, L1) which momentarily corresponds to the resonance frequency of the reactive element which varies during a working operation. The first control circuit (7) is constructed to control momentary frequency in dependence on momentary phase difference between the current and voltage values of the alternating voltage.