Abstract: A voltage equalizing apparatus for battery devices includes a core, a plurality of first battery devices interconnected in series with each other, each consisting of one or more cells, a plurality of secondary windings magnetically connected with each other through the core, a plurality of first switching devices, each connected to one of the plurality of secondary windings and one of the plurality of first battery devices to constitute a first closed circuit, one or more second battery devices provided separately from said plurality of first battery devices interconnected in series or a second battery device provided by rendering the whole of said plurality of first battery devices interconnected in series one battery device, a primary winding magnetically connected with the plurality of secondary windings through the core, and a second switching device connected in series with the second battery device and the primary winding to constitute a second closed circuit.