PURPOSE: To make the sputtering rate and quality of a film constant by providing a means for controlling the coil voltage or current of a magnetron-discharge electromagnet to allow the peak-to-peak voltage of an electrode to coincide with a set value.

CONSTITUTION: A high-frequency peak-to-peak voltage detecting circuit 3 is arranged between a terminal 8 connected to a target and an impedance-matching circuit 2. The detection value and a reference value set by a high-frequency peak-to-peak voltage setting circuit 5 are compared by a comparator 4, and the difference between both values is outputted to a control circuit 6. The control circuit 6 is actuated to decrease or increase the coil current of the magnetron-discharge electromagnet, hence the peak-to-peak voltage is increased or decreased. By this method, the reproducibility in the sputtering rate and quality of a film is improved regardless of the change in the erosion of the target.