A film forming apparatus 1 includes a plasma generating mechanism 47 commonly used for plasmarizing a processing gas and a cleaning gas supplied into a processing vessel 11 in which a vacuum atmosphere is formed; an exhaust device 17 configured to evacuate an exhaust line 61 connected to a processing gas discharge unit 43 while the plasmarization of the cleaning gas is being performed by the plasma generating mechanism 47; a tank 62 provided at the exhaust line 61; and a valve V2 which is provided at the exhaust line 61 between the tank 62 and the processing gas discharge unit 43. The valve V2 is configured to be closed to reduce an internal pressure of the tank 62 and opened to attract the plasmarized cleaning gas into the tank 62 from a processing space 40 through the processing gas discharge unit 43.