In the above-described embodiment, a so-called series-parallel converter that includes the four switching elements and that is able to switch between series connection and parallel connection is described as the electric power converter 11; however, the electric power converter is not limited to this configuration. In short, as long as an electric power converter that includes two step-up/step-down circuits, which are operated in parallel with each other, with such a circuit configuration that switching elements are turned on or off in accordance with the logical addition of PWM signals of these step-up/step-down circuits, the invention is applicable.

FIG. 15 shows an alternative embodiment of the electric power converter 11. The electric power converter 11 includes three series-connected arms from the high-voltage line 26 toward the reference line 28.

In addition, the first battery B1 is connected between the connection point 40 and the reference line 28. The connection point 40 is provided between the second arm and the third arm from the high-voltage line 26 side. In addition, the first reactor L1 is provided in series with the first battery B1, and the first capacitor C1 is provided in parallel with the first battery B1.

The second battery B2 is connected between the connection point 42 and the reference line 28. The connection point 42 is provided between the first arm and the second arm from the high-voltage line 26 side. In addition, the second reactor L2 is provided in series with the second battery B2, and the second capacitor C2 is provided in parallel with the second battery B2.