An access device and method for preventing transmission of copyrighted contents to an external network and a method for the same. The access device includes a packet-header analyzer (310) analyzing a header of a packet (400) received from a home network device, a copyrighted-content sensor (340) detecting whether the packet (400) includes copyrighted content as a result of the analysis, an address converter (320) for converting a packet source IP address (420) into an IP address supported by the external network if a packet destination address (430) is an external network address as a result of the analysis, a mapping-table generator (350) generating a mapping table for managing a mapping a relationship between the packet source IP address (420) and the converted IP address, and a packet transmitter (330) transmitting the packet (400) to the IP address supported by the external network and discarding the packet (400) to block transmission of the copyrighted content to the external network if the copyrighted-content sensor (340) detects that the packet (400) includes the copyrighted content.