A power supply system comprising: a plurality of power storage units (12a to 12d) that are chargeable and dischargeable; a plurality of voltage converters (24a to 24d) having input sides connected to the plurality of power storage units, respectively, and output sides connected in parallel to each other, the voltage converters being configured to convert voltages (V1 to V4) of the plurality of power storage units connected to the input sides at arbitrary voltage conversion ratios (Tr), and output the converted voltages to the output sides; and a plurality of current measuring instruments (26a to 26d) connected to the input sides of the plurality of voltage converters, respectively, and configured to measure currents (11 to I4) flowing from the plurality of power storage units to the input sides, the power supply system further comprising: a power storage unit determination unit (18, 46) configured to determine at least one of the plurality of power storage units as a reference power storage unit to be charged and determine remaining ones of the plurality of power storage units as remaining power storage units to be discharged; characterized in that the power supply system further comprises: a current difference determination unit configured to determine a current difference between the currents flowing from the remaining power storage units and the current flowing from the reference power storage unit, based on the currents measured by the plurality of current measuring instruments; and a voltage conversion ratio determination unit configured to determine a voltage conversion ratio of the voltage converters connected to the remaining power storage units, based on the determined current difference. a plurality of power storage units (12a to 12d) that are chargeable and dischargeable; a plurality of voltage converters (24a to 24d) having input sides connected to the plurality of power storage units, respectively, and output sides connected in parallel to each other, the voltage converters being configured to convert voltages (V1 to V4) of the plurality of power storage units connected to the input sides at arbitrary voltage conversion ratios (Tr), and output the converted voltages to the output sides; and a plurality of current measuring instruments (26a to 26d) connected to the input sides of the plurality of voltage converters, respectively, and configured to measure currents (11 to I4) flowing from the plurality of power storage units to the input sides, the power supply system further comprising: a power storage unit determination unit (18, 46) configured to determine at least one of the plurality of power storage units as a reference power storage unit to be charged and determine remaining ones of the plurality of power storage units as remaining power storage units to be discharged; characterized in that the power supply system further comprises: a current difference determination unit configured to determine a current difference between the currents flowing from the remaining power storage units and the current flowing from the reference power storage unit, based on the currents measured by the plurality of current measuring instruments; and a voltage conversion ratio determination unit configured to determine a voltage conversion ratio of the voltage converters connected to the remaining power storage units, based on the determined current difference. a current difference determination unit configured to determine a current difference between the currents flowing from the remaining power storage units and the current flowing from the reference power storage unit, based on the currents measured by the plurality of current measuring instruments; and a voltage conversion ratio determination unit configured to determine a voltage conversion ratio of the voltage converters connected to the remaining power storage units, based on the determined current difference.