Disclosed is a technology by which rules on communication permission or control are enforced to network internal devices such that an environment which looks as if to have a virtual firewall existing between network internal devices can be established. A communication control apparatus for this is located on the same level in the network as other devices are located. By using this communication control apparatus, an address resolution protocol (ARP) packet in which a data link layer address is manipulated is provided to devices that are the objects of communication cut-off, such that data packets transmitted by the communication cut-off object devices are transmitted to manipulated abnormal addresses. By doing so, communication with the communication cut-off object devices is cut off. For a device which is in a communication cut-off state although the device is not an object of communication cut-off any more, the communication control apparatus transmits an ARP packet including normal address information to the device such that the communication cut-off state is canceled.