A power supply system includes a main power storage device (BA) and a plurality of sub power storage devices (BB1, BB2). A converter (12B) is connected to selected one of the sub power storage devices (BB1, BB2) to convert voltage between the selected sub power storage device and an electric power feeding line (PL2) bidirectionally. When a request for switching the selected sub power storage devices in use is generated, a converter (12A) steps up voltage on the electric power feeding line (PL2) to a predetermined voltage, and thereafter a process for switching relays (SR1, SRIG, SR2. SR2G) is performed. The predetermined voltage is higher than any of a voltage output from the main power storage device (BA) and a voltage output from a sub power storage device to be newly connected to the converter (12B). 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.