A communication apparatus used in a plurality of networks is disclosed. The communication apparatus includes a firewall which allows communication with outside of the communication apparatus when disabled, and prohibits communication with outside of the communication apparatus when enabled. Then, the communication apparatus includes a firewall control unit which acquires a first MAC address of a first default gateway provided for a predetermined specific network and a second MAC address of a second default gateway provided for a network in which the communication apparatus is being connected, and controls the firewall according to a result of comparison of the first MAC address and the second MAC address.