Disclosed is a technique which can share single public Internet protocol without a network address translation when a plurality of computers use the Internet through an Internet access gateway. The Internet access gateway according to the invention includes a local network access point which is connected to a local network for either inputting or outputting a packet either to local network or therefrom; an Internet access point which is connected to the Internet for either inputting or outputting the packet either to the Internet or therefrom; a port translation table for storing nodes having one Internet protocol address, public port numbers corresponding to each of the nodes, a local port number corresponding to each of the nodes, and a media access control (MAC) address corresponding to each of the nodes; and an address translation processor for changing a public port number using a local port number and the MAC address included in an Internet protocol packet as delimiters in a predetermined assigning manner when the Internet protocol packet is received at the local network, storing a changed public number in the port translation table, for a public port number corresponding to an Internet protocol packet with reference to the port translation table when the Internet protocol packet is received at the Internet, and searching for a local port number corresponding to the public port number.