In a network communication system enabling copying and mutual reflection of definition information among a plurality of systems interconnected over a backbone network, each of the plurality of systems has a host control unit for transferring definition information for communication with other system and manipulating received definition information, and a database for storing manipulated definition information. The host control unit includes an element for acquiring predefined network definition information for use in communication intended for copying, an element for copying definition information from a distributor-side system for distributing definition information, an element for referencing the copied definition information so as to specify a connection form of a communication resource governed by said distributor-side system, and an element for using the acquired network definition information to set communication path information concerning the distributor-side system in the copied definition information according to the specified connection form of a communication resource. Definition information manipulated by these elements is stored in the distributor-side system. Communication with the distributor-side system is effected based on the definition information. This configuration enables one system to share network definition information with other systems and permits reduction of a load of system management resulting from modification of definition information. The above network operation mode can apply to any network constructed to have a network topology of a LAN, WAN, or the like.