A DC-DC converter is configured with a voltage-source power converter provided at a primary side of a transformer, a current-source power converter provided at a secondary side of the transformer, and a controller. The controller generates a first control input based on a voltage between input and output terminals of the voltage-source power converter, a second control input based on a voltage between input and output terminals of the current-source power converter, and a command value for PWM or PFM control based on the first and second control inputs and an input-output current flowing between one of the input and output terminals of the voltage-source power converter and the current-source power converter. Therefore, it is easy to switch between a powering state and a regenerating state in the DC-DC converter.