Apparatus identification information about wireless access apparatuses judged to be able to communicate with a monitoring apparatus, among multiple wireless access apparatuses, is stored in a neighborhood database. If there is apparatus identification information that is not stored in the neighborhood database, among apparatus identification information stored in a registration database in which apparatus identification information about wireless access apparatuses registered as monitoring targets of the monitoring apparatus is stored, it is judged again for a wireless access apparatus to which the apparatus identification information is given whether communication is possible, after a predetermined time elapses. On the other hand, if there is no such apparatus information, or if the judgment is performed again for a predetermined number of times, the apparatus identification information stored in the neighborhood database is copied to the registration database.