A power supply apparatus for a vehicle includes first and second batteries provided electrically in parallel to main loads, a boost converter provided between the first battery and the main loads, a boost converter provided between the second battery and the main loads, an auxiliary battery, a DC/DC converter, and an auxiliary load driven by power from the auxiliary battery or DC/DC converter. The controller determines charging currents or discharging currents for the batteries reflecting variations in a current flowing through the auxiliary load. Accordingly, a power supply apparatus for a vehicle can thus be provided in which imbalance between charging/discharging currents for a plurality of power storage devices is reduced.