A network monitoring system which monitors activities on a network with optimal coverage and frequency, depending on the current state of the network. A monitoring policy setting unit sets a specific monitoring policy that includes: which object to watch, which item of that object to monitor, and how frequent it should be. According to this policy, a monitoring unit carries out monitoring of the network. The monitoring result is passed to a monitoring policy changing unit, which changes the current monitoring policy being set in the monitoring policy setting unit. Some related resources on the network may also be reconfigured according to the reported monitoring result, by a resource setup changing unit. An event detector detects a particular event occurred in the network resources and notifies the monitoring policy changing unit of the occurrence, so that the monitoring policy will be changed accordingly.