1. A method of monitoring a network, the network including: a plurality of units to be monitored, each of which holds managed objects reflecting states to be monitored; and a network management system which is allowed to access a managed object of each of the plurality of monitored units through a predetermined network management protocol, the method comprising: implementing an additional managed object representing the states of a plurality of managed objects of a monitored unit in each of the plurality of monitored units, the additional managed object implemented by aggregating all the states of the plurality of managed objects into a single value; and storing the single value as a value of the additional managed object so as to be readable by the network management system.