To stabilize a sputtering rate by preventing abnormal discharge, to suppress the formation of particles caused by abnormal discharge, and to prevent the transition of stable thin films of metal oxide into metal films.

In the sputtering film deposition system where gaseous O2 as a reactive gas and gaseous Ar as an inert gas are introduced, and thin films of tantalum pentoxide as metal oxide are deposited on substrates 12a and 12b by reactive d.c. sputtering, a control part 21 controls a variable power source 15, and breaks film deposition electric power fed to a target 14 at a prescribed breaking cycle for a prescribed breaking time.