A first direct-current power converter circuit increases an electrical potential difference between a positive electrical potential of a load and a positive electrical potential of a power source by a step-up operation, and a second direct-current power converter circuit increases an electrical potential difference between a negative electrical potential of the load and a negative electrical potential of the power source by a step-up operation. A control device controls switching operations of first and second switching devices included in the first direct-current power converter circuit based on a first duty. The control device controls switching operations of third and fourth switching devices included in the second direct-current power converter circuit based on a second duty. The control device controls a load voltage to be an arbitrary voltage, which is equal to or more than a source voltage.