A voltage transform part transforms the direct-current power input to an input part. A first input and output part outputs the transformed direct-current power to a battery unit and to which direct-current power is input from the battery unit. A conversion part converts the direct-current power input to the input part into alternating-current power. A second input and output part outputs the alternating-current power to a power system or a load and to which an alternating-current power is input from the power system. The conversion part converts the alternating-current power input to the second input and output part into direct-current power. The second voltage transform part transforms the direct-current power converted by the conversion part and transforms the direct-current power input to the first input and output part. The conversion part converts the direct-current power transformed by the second voltage transform part into alternating-current power.