A computer system includes multiple ports to which at least one external device is connected and which are connectable to multiple power supplying lines branched from a power supplying line for supplying electric power to the at least one external device; a switching unit which controls connections between the power supplying lines and the ports; and a controller which controls the switching unit so that two or more power supplying lines among the power supplying lines are connected to a first port, to which one of the at least one external device is connected, among the ports.