In a routing process based on contents of a communication, there is a problem that it is required to carry out switching to refer to the contents every switch on a route or use a routing label. In order to solve the problem, a relay unit terminates data from a transmission source terminal and transfers the contents to a network controller. The network controller assigns flow data which is necessary for relay and issues a flow transfer instruction to a switch. The assigned flow data is notified to the relay unit and the relay unit sets a communication flow to a destination terminal by using the specified flow data, and relays the data to the destination terminal from the transmission source terminal.