In a network relay router 10, a multicast routing protocol processing module 11A sequentially sends a join request message (CP1) to a router 30a functioning as a rendezvous point via an interface 101, based on the settings of a multicast group address or destination address and a sender VRF name. The network relay router 10 receives a multicast packet (DP1) from the router 30a via the interface 101 and acquires a sender address or source address of a transmission device SE from the received multicast packet. The network relay router 10 sends a join request message (CP2) via an interface 102 on the side of the transmission device SE and receives a multicast packet via the interface 102. This establishes an optimum multicast route (MR) between the transmission device SE and the network relay router 10.