A power conversion system includes an AC to DC conversion circuit, a voltage detector, a step-down chopper circuit, a power conversion device for auxiliary power sources, and a control unit. The AC to DC conversion circuit converts AC power supplied from overhead wires via a transformer into DC power. The voltage detector detects a voltage of AC power supplied from the transformer. The step-down chopper circuit steps down the voltage of DC power produced through conversion by the AC to DC conversion circuit. The power conversion device for auxiliary power sources converts the DC power stepped down by the step-down chopper circuit into power for driving loads mounted in an electric vehicle and supplies it to the loads. The control unit controls the AC to DC conversion circuit and the step-down chopper circuit such that the voltage of AC power detected by the voltage detector approaches a reference voltage.