To solve the problem that in a packet communication system including a multi-address function with respect to conventional groups of terminals, it is necessary for all multicast routers to hold and manage an output link list for a number of multicast addresses, so that the quantity of management information for multicast delivery and management processes become huge.

A multi-address group management router transmits a multi-address packet while adding an arithmetic address with which a delivery destination can be calculated by arithmetic, thereto and an arithmetic address operation router determines the delivery destination by operating the arithmetic address, thereby performing multi-address communication. Thus, the quantity of multi-address group management information and management processes can be reduced.