First and second capacitors are connected in series between positive/negative electrodes of a DC power source. A first terminal of a reactor and a first terminal of an electric power system are connected to the interconnection point between the first and second capacitors. A first switch section has first and second terminals respectively connected to the positive electrode of the DC power source and a second terminal of the reactor. A second switch section has first and second terminals respectively connected to the negative electrode of the DC power source and the second terminal of the reactor. A third switch section has first and second terminals respectively connected to the second terminal of the reactor and a second terminal of the electric power system. A fourth switch section has first and second terminals respectively connected to the second terminal of the reactor and the second terminal of the electric power system.