An apparatus forms a plated film in fine trenches and plugs for interconnects and in the openings of a resist formed in the surface of a substrate such as a semiconductor wafer, and forms bumps (protruding electrodes) on the surface of a semiconductor wafer. The apparatus includes a substrate holder capable of opening and closing for holding a substrate such that the front surface of the substrate is exposed while the backside and the edge thereof are hermetically sealed. A plating tank accommodates a plating liquid in which an anode is immersed. A diaphragm is provided in the plating tank and disposed between the anode and the substrate held by the substrate holder. Plating liquid circulating systems circulate the plating liquid to respective regions of the plating tank, separated by the diaphragm. A deaerating unit is disposed in at least one of the plating liquid circulating systems.