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. In the case of a switching-forced region where the SOC of the selected sub power storage device in use is lower than a lower limit reference value, the sub power storage device is forced to be switched regardless of the vehicle's state. In contrast, in the case of a switching-permitted region where the SOC is higher than that in the switching-forced region, a switch request is generated based on the vehicle's state under the condition that does not influence the vehicle's drivability.