PURPOSE: To deal with the troubles of a network in the order of higher importance toy providing an alarm level table to register the alarm levels of the network and displaying the higher alarm levels with preference among a large number of alarms which are collected in occurrence of the faults.

CONSTITUTION: The alarm levels of a network 1 are registered on an alarm level table 6. A collection means 3 collects the device and line alarms through a collection network when the alarms of its own devices and the alarms of the connected connection lines are transmitted from every transmission device of the network 1 if the faults occur. Then an importance display means 4 refers to the table 6 to sort the collected device and line alarms in the order of higher alarm levels and then displays the trouble information on the device or line alarms on a screen also in the order of higher alarm levels. In such a constitution, the decision of fault parts can be supported in the network 1.