A power control device for a power supply mounted on a vehicle is provided, which includes a generator mounted on the vehicle and configured to regenerate power from kinetic energy of the vehicle, a high-voltage battery configured to accumulate the power regenerated by the generator, a low-voltage battery of which a nominal voltage is lower than the high-voltage battery, a voltage converter configured to lower an output voltage from the high-voltage battery and charge the low-voltage battery at the lower voltage, and a controller configured to control the voltage converter. The controller operates the voltage converter to start the charging of the low-voltage battery after the vehicle is powered ON and before an engine mounted on the vehicle is started.