1. An apparatus comprising: a generation device which generates communication availability information indicating availability of communication between a plurality of transmitters and a plurality of destinations in a communication network having a communication function in a hierarchical structure of a plurality of layers, the availability of communication being obtained on each layer of the plurality of layers, before and after a communication state between a transmitter and a destination-changes from available to unavailable; an identification device which identifies a first device and a layer as a cause of fault by repeating, layer by layer starting from a search starting layer toward a lower layer in the hierarchical structure of the plurality of layers, processes of dividing the communication network into a plurality of affected ranges being affected by the fault in each of the plurality of layers, so that a communication is available between any devices within each of the affected ranges in each of the plurality of layers and unavailable between any devices across two of the affected ranges in each of the plurality of layers, by comparing the communication availability information before and after the communication state changes and grouping destinations in paths where the communication state has changed from available to unavailable, and deducing an interface of a second device located at a border between the affected ranges as a fault occurrence point, wherein the plurality of layers include an application layer, a transmission control protocol/user datagram protocol layer, an Internet protocol layer, a media access control layer and a physical layer.