Included are a second control circuit 52A, which carries out fixed frequency control of a second bridge circuit 23 based on the voltage and current of a first direct current voltage supply 11, and a first control circuit 51, which carries out PFM control of a first bridge circuit 13 based on the voltage and current of a second direct current voltage supply 21. The first control circuit 51 carries out PFM control of the first bridge circuit 13 at a frequency equal to or lower than the resonance frequency of an LC resonant circuit 14 in accordance with a control amount based on the voltage and current of the second direct current voltage supply 21 when power is supplied from the first direct current voltage supply 11 to the second direct current voltage supply 21, and the second control circuit 52A carries out fixed frequency control of the second bridge circuit 23, using phase shift control or the like, in accordance with a control amount based on the voltage and current of the first direct current voltage supply 11 when power is supplied from the second direct current voltage supply 21 to the first direct current voltage supply 11.