To provide a highly reliable mutlicast distribution source switching control technique for properly switching a distribution source of a multicast stream.

A table 12 for storing a switching system state stores an IP multicast address, a transmission source IP address, a switching system state, and an IP address of a distribution server accommodating router. A switching control means 11 is provided with a means for performing transfer setting or interruption setting for each multicast address set consisting of a combination of the IP multicast address and transmission source IP address for packet filters of distribution server accommodating routers 3, 4, sets transfer to the packet filter of the distribution server accommodating router for the multicast address set in which the switching system state is switched from a standby system to an active system by the table 12, and sets interruption for the packet filter of the distribution server accommodating router for the multicast address set in which the switching state is switched from the active system to the standby system.

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