A first flying capacitor circuit and a second flying capacitor circuit are connected in series so as to be in parallel to a high voltage side DC part. A reactor is connected to a positive side terminal of a low voltage side DC part and a midpoint of the first flying capacitor circuit. A midpoint of the second flying capacitor circuit is connected to a negative side terminal of the low voltage side DC part. A node between the first flying capacitor circuit and the second flying capacitor circuit is connected to an intermediate potential node of the high voltage side DC part.