An extraction unit 141 extracts predetermined pieces of information from each of a plurality of packets and sent from equipment 20. Then, an inference unit 142 infers a piece of equipment information that is information on the equipment 20, for each of the plurality of packets on the basis of the pieces of information extracted by the extraction unit 141. Then, the first selection unit 143 selects a predetermined piece of equipment information for each packet type from among pieces of equipment information on the basis of a level of detail of each piece of equipment information. Then, the second selection unit 144 selects, on the basis of a level of reliability predefined according to each packet type, a predetermined piece of equipment information corresponding to the equipment 20 from among pieces of equipment information inferred by the first selection unit 143.