An object to be processed (e.g., semiconductor wafer W) having a recess formed in a surface thereof is placed on a stage 34 disposed in a processing vessel 24 capable of being vacuumized. Thereafter, a plasma is generated in the processing vessel 24, so that a metal target 70 is ionized by the plasma to generate metal ions in the processing vessel 24. Then, a thin film is deposited on the surface of the object to be processed including a surface in the recess, by supplying a bias power to the stage 34 so as to draw the metal ions into the object to be processed placed on the stage 34 by the supplied bias power. In the present invention, a wattage of the bias power is varied within a range in which the surface of the object to be processed is not substantially sputtered.