To enable network terminals holding a default IP address in common to each other in advanceare to be connected to a network to make a communication with each other without revising their internal configurations.

A console terminal 22 assigns different IP addresses to Ethernet (R) ports 12 to 14 of an Ethernet (R) switch 100 via a serial port 11 in advance, the IP address of a packet from terminals 19 to 21 connected to the Ethernet (R) ports 12 to 14 or the IP address to the terminals 19 to 21 is converted into the IP address assigned to the ports to attain communication between the terminals to which the same IP address is assigned.