In an FDB provided for a switch, line information associated with MAC address information is managed separately for sending destination line information and receiving discrimination line information, and provides an incompatibility permission flag of permitting that they are different. Also, a function of rewriting the sending destination line information with a command from a manager is provided and linked with the change of the incompatibility permission flag. While the traffic is moved to a new line at the time of the line switching, this incompatibility is permitted, and even if a frame is received from an old line, the receiving line is not updated based on the frame.