The lower-level information acquirer searches a lower-level network, and acquires lower-level addresses for air-conditioning devices that are connected to the lower-level network. A database generator searches an upper-level network, and generates a database of upper-level addresses of air-conditioning devices that are connected to the upper-level network. An address assigner references the database generated by the database generator, and assigns vacant addresses existing among the upper-level addresses of the upper-level network to air-conditioning devices that are connected to the lower-level network. The table generator generates an address conversion table for converting the upper-level addresses assigned by the address assigner to lower-level addresses acquired by the lower-level information acquirer.