A power supply system includes a main power storage device and a plurality of sub power storage devices. A converter is connected to selected one of the sub power storage devices to convert voltage between the selected sub power storage device and an electric power feeding line bidirectionally. When a request for switching the selected sub power storage device in use is generated, a converter steps up voltage on the electric power feeding line to a predetermined voltage, and thereafter a process for switching relays is performed. The predetermined voltage is higher than any of a voltage output from the main power storage device and a voltage output from a sub power storage device to be newly connected to the converter. Further, during the process for switching connection of the relays, upper limits on electric power input/output to/from the selected sub power storage device are set to 0.