An apparatus for surface treatment, especially for etching and/or coating workpieces by ion bombardment is described. This apparatus comprises at least one ionization chamber having at least one hot cathode, gas atoms being introduced into this chamber for the low-voltage arc-discharge between the ionization chamber and at least one anode inside the treatment chamber connected to a vacuum pump. At least one magnet coil mounted within the treatment chamber is used to control the ion density of the low-voltage arc-discharge and is mounted inside the treament chamber. The workpieces to be treated are arranged outside these magnet coils. Homogeneous surface treatment of the workpieces is ensured by the selected arrangement of magnet coils and workpieces.