A gateway device including: a plurality of control units configured to respectively notify first data received from the plurality of communication devices or/and second communication networks and notify the plurality of communication devices or/and second communication networks of second data; and a data analysis and management unit configured to analyze data received from the first communication network and notify a control unit included in the plurality of control units of a result of the analysis, the control unit being related to result of the analysis, and analyze the first data received from the plurality of control units respectively and notify the first communication network, the data analysis and management unit generating a plurality of local MAC addresses from a MAC address given to the gateway device and assigning the local MAC addresses to the plurality of control units.