A network management apparatus acquires a given information object related to a plurality of occurrence paths of a failure in a logical layer of a network configuration; and retrieves, as a candidate of a facility to be a failure cause, information objects related to the facility layer and the physical layer commonly associated with the given information object; calculates, for each of the retrieved information objects, the number of information objects which are associated with the object and which are related to the plurality of occurrence paths of the failure as a multiplicity; and calculates, for each of the retrieved information objects, a proportion of the multiplicity with respect to the number of information objects in the logical layer which are affected when the failure occurs in the object.