A network system is provided, in which a system change can be easily performed by adding or exchanging an equipment(s) to be controlled or monitored. The equipment has an object with an object identifier defined according to a service content provided by the equipment. Upon the receipt of a service request using the object identifier from a network device connected to the equipment via a network, the equipment executes the service defined in the object according to this service request. By assigning a same object identifier to objects of a plurality of equipments, it is possible to provide the same service from those equipments according to the service request performed from the network device by use of the same object identifier.