A first L2SW acquires a correspondence relation between a multicast group and a representative IP address retained in a snooping table of a second L2SW through a control plane, and registers the correspondence relation to a snooping table of the first L2SW. When the first L2SW receives a multicast packet whose destination is a multicast group, the first L2SW extracts a corresponding representative IP address of the other L2SW based on the snooping table of the first L2SW, and converts the multicast packet into a unicast packet whose destination is the extracted representative IP address. When the destination representative IP address contained in the unicast packet is its own representative IP address, the second L2SW converts the unicast packet into multicast packets.