To reduce the loads of routing calculation and to perform a high-speed routing processing by executing the decision processing of an optimum route from the origin node of a data transmission line to a destination node.

A protocol control part 13 analyzes a received connection setting request and supplies originating and terminating addresses and QOS to a routing control part 14, the optimum route from a source node to the destination node is decided and the request for using a resource is supplied to a resource management part 12. In the case of being capable of securing the resource there, 'OK' is returned to the routing control part 14 and then, the connection of a terminal equipment T1 and a switch A11 is set. The protocol control part 13 sends out a connection setting request message to the switch A11, supplies it to a work station WS2 and transfers the connection setting request message to the next switch. By repeating such processings and the connection of the optimum route between the terminal equipments is established.