A DC/DC conversion circuit is configured with a first power converter and a second power converter that are connected through an insulation transformer, and performs power transition bidirectionally between two DC-voltage sources. In the case of charging the DC-voltage source in the side where the second power converter is placed, a control is made using a first rectifier-control mode in which the first power converter is placed under an output variable control according to an inverter operation and the second power converter is operated according to a rectifier operation. Then, when a charging current becomes an upper limit value or more, a control is made by switching the mode to a first inverter-control mode in which the first power converter is placed under an output fixed control according to the inverter operation and the second power converter is placed under an output variable control according to the inverter operation.