A thin film is fabricated while causing ions in a plasma P to be incident by effecting biasing relative to the space potential of the plasma P by imparting a set potential to the surface of a substrate 9. A bias system 6 causes the substrate surface potential Vs to vary in pulse form by imposing an electrode imposed voltage Ve in pulse form on a bias electrode 23 which is in a dielectric block 22. The pulse frequency is lower than the oscillation frequency of ions in the plasma P, and the pulse period T, pulse width t and pulse height h are controlled by a control section 62 in a manner such that the incidence of ions is optimized. The imposed pulses are controlled in a manner such that the substrate surface potential Vs recovers to a floating potential Vf at the end of a pulse period T, and that the ion incidence energy temporarily crosses a thin film sputtering threshold value in a pulse period T.