In a firewall device protecting a specific network against an attack from an external network, a filtering object identifying portion identifies whether or not received data includes filtering object data, a filtering execution/inexecution selector transmits to a source device of the received data, when the received data includes the filtering object data, a selection request of a desire for a filtering execution or inexecution of the received data, does not select the filtering execution of the received data from the source device on a condition that a selection response indicates a desire for the filtering inexecution and the source device is authenticated, but selects the filtering execution under other conditions, and a filtering processor filters the selected received data.