To dynamically join/leave a terminal to/from a multicast group from a transmission source permitted by a network administrator in response to a request from the terminal without modifying the terminal capable of making only a joint request to a multicast group from an unspecified transmission source server in a multicast network which can join only a multicast group from a specified transmission source.

A multicast transmission source address table 220 calculates a transmission source server permitted by the network administrator of the multicast network on the basis of a multicast group address and a line 116 on which a joint request takes place included in the joint request to the multicast group from a terminal 100 supporting only a transmission source non-limited multicast so that a multicast router 110 translates the joint request to the transmission source non-limited multicast group into a joint request to the multicast group from the transmission source server permitted by the network administrator.