A power supply system comprising: a main line configured to energize at least electric power input from outside; a plurality of sweep modules connected to the main line in series; and a controller (2, 11), wherein each of the plurality of sweep modules includes a battery module including at least one battery, and an electric power circuit module including at least one switching device (41, 42) that switches a connection state between the battery module and the main line between connection and disconnection, wherein the switching device of the electric power circuit module includes a first switching device attached to the main line in series and attached to the battery module in parallel, and a second switching device disposed in a circuit that connects the battery modules to the main line in series, the controller is configured to perform the sweep control by sequentially outputting, to each of the plurality of sweep modules, the gate signal for controlling alternate driving of turning the first switching device and the second switching device on and off, at every predetermined delay time, and the controller is configured to perform a first process of performing sweep control of sequentially switching the battery module connected to the main line among the plurality of battery modules by outputting a gate signal for controlling the switching device to the electric power circuit module, characterized in that the controller is further configured to perform a second process of performing the sweep control by detecting an SOC in each of the battery modules while electric power is input from outside through the main line, by disconnecting, from the main line, a high SOC module that is the battery module whose detected SOC level satisfies a high SOC condition, and by excluding the sweep module including the high SOC module, and the controller is configured to output, to the sweep module including the high SOC module, a signal for keeping the first switching device in an on state and the second switching device in an off state in disconnecting the high SOC module from the main line. a main line configured to energize at least electric power input from outside; a plurality of sweep modules connected to the main line in series; and a controller (2, 11), wherein each of the plurality of sweep modules includes a battery module including at least one battery, and an electric power circuit module including at least one switching device (41, 42) that switches a connection state between the battery module and the main line between connection and disconnection, wherein a battery module including at least one battery, and an electric power circuit module including at least one switching device (41, 42) that switches a connection state between the battery module and the main line between connection and disconnection, wherein the switching device of the electric power circuit module includes a first switching device attached to the main line in series and attached to the battery module in parallel, and a second switching device disposed in a circuit that connects the battery modules to the main line in series, a first switching device attached to the main line in series and attached to the battery module in parallel, and a second switching device disposed in a circuit that connects the battery modules to the main line in series, the controller is configured to perform the sweep control by sequentially outputting, to each of the plurality of sweep modules, the gate signal for controlling alternate driving of turning the first switching device and the second switching device on and off, at every predetermined delay time, and the controller is configured to perform a first process of performing sweep control of sequentially switching the battery module connected to the main line among the plurality of battery modules by outputting a gate signal for controlling the switching device to the electric power circuit module, the controller is further configured to perform a second process of performing the sweep control by detecting an SOC in each of the battery modules while electric power is input from outside through the main line, by disconnecting, from the main line, a high SOC module that is the battery module whose detected SOC level satisfies a high SOC condition, and by excluding the sweep module including the high SOC module, and the controller is configured to output, to the sweep module including the high SOC module, a signal for keeping the first switching device in an on state and the second switching device in an off state in disconnecting the high SOC module from the main line.