An information processing system includes a switch device including a plurality of ports; and a control device configured to: specify a flow in which a transmission port is to be changed among the plurality of flows, and a transmission port after the change, by referring to load distribution information that associates flow information and port information with each other and statistics information indicating use rates of the ports, and transmit a changing instruction packet including information of the specified flow and the port after the change, for instructing the switch device to change the transmission port to the switch device, wherein the switch device is configured to update information in header information, which each of the series of packets included in the specified flow includes, so as to become information with which the port after the change is selected, when the changing instruction packet is received from the control device.