To provide a multicast distribution system capable of selecting a communication route satisfying communication characteristics requested by a multicast group and executing multicast distribution.

In a mesh virtual network wherein a plurality of routers R are connected, the router Rs executes the multicast distribution to the multicast group corresponding to an application. When a CPU load rate and the communication characteristics (band width and communication delay) of the multicast group exceed a threshold, the router Rs updates the number of branches and depth of a multicast tree for distributing packets from the router Rs and starts the reconstruction of the multicast tree. When constructing the multicast tree, the router Rs refers to the route characteristics (band width and communication delay) of the mesh virtual network and preferentially selects the communication route with a margin in the route characteristics. The router Rs generates a routing table 10 on the basis of the multicast tree.