Multicast traffic is transferred, via routers, from a sender to receivers through a delivery tree that is determined based on a multicast routing protocol and includes delivery paths each communicably coupling the sender and one receiver. A router includes a multicast routing table used for transferring the multicast traffic through the delivery tree. The router generates delivery path information on first and second delivery paths each communicably coupling the sender and the router. Upon detecting a link failure on the first delivery path, the router performs delivery-path change processing that switches a first pair of interfaces along the first delivery path to a second pair of interfaces along the second delivery path without waiting for the multicast routing table being updated using the multicast protocol, and transmits a delivery-path change message to routers along the second delivery path so that the routers perform the delivery-path change processing.