Provided is a network address translation (NAT) apparatus including: a NAT unit translating an address so as for a client and a server to communicate with each other through an outside network by referring to a NAT table that manages an inside IP address and an outside IP address mapped to the inside IP address; and a cookie proxy unit providing a cookie to the client by referring to a connection cookie table that manages a cookie corresponding to the outside IP address when there is a cookie request from the client.