A communication system comprises a plurality of network elements and a management apparatus. Each of the network elements transfers a data signal. The management apparatus manages a line service provided by a network element as management object among the plurality of network elements. The management apparatus generates an authentication code corresponding to the network element as management object and notifies the generated authentication code to the network element as management object. The network element as management object, using the notified authentication code, judges whether or not to accept a change concerning the line service of the own network element.