PURPOSE: To eliminate the damage due to an abnormal discharge by adjusting the flow rate of an active gas on receipt of a signal for controlling the amt. of the active gas to be introduced when an abnormal discharge is generated.

CONSTITUTION: Gaseous Ar as a discharge gas and gaseous N2 as an active gas are introduced into a film forming chamber 1 provided with a target 3 in the sputtering device. The electrical characteristics of the discharge in the film forming process are detected by detectors 8 and 9. The data detected by the detectors 8 and 9 are compared with the prepared reference data by a comparator 10 to judge whether the discharge is normal or not. When the discharge is judged as abnormal by a controller 11, a signal is issued to control the amt. of the active gas (N2) to be introduced. The flow rate of the active gaseous N2 is adjusted by a flow controller 7 on receipt of the control signal. As a result, the generated abnormal discharge is rapidly returned to normal.