To construct a communication network system capable of reducing resources and eliminating the need for monitoring a multiplex system on the network by allowing a stand-by system to execute call connection by the node name of an operating system in network connection based on the setting of a node name when a fault occurs in the multiplex system and operation is switched to the stand-by system.

When a program operated by an operating system 11 is switched to a stand-by system 12 in a certain node (multiplex system 1) due to the occurrence of a fault, the node name of the system 11 is set up only when the stand-by system 12 of the node connects a network call based on the node name, so that a data link between the multiplex system 1 and a node setting up the system 1 as a network connection destination is established.