An open flow network system is stabilized while reducing a load, by reducing inquiries of a flow entry to a controller about a flow in which a flow registration has not completed. Specifically, the controller registers the flow entry that defines a rule and an action to uniformly control packets as a flow in a flow table of a switch. When receiving a packet, the switch carries out an inquiry of the flow entry corresponding to the received packet to the controller, if the flow entry corresponding to the received packet is not registered on the flow table, and stacks the received packet. Also, the switch controls the transfer of the received packet which has the same header data as the stacked packet by using the stacked packet until the flow entry corresponding to the received packet is registered.