The multicast communication scheme which can enable a user to easily comprehend the multicast groups existing on the network, easily carry out an operation to join a desired multicast group, and easily specify a desired communication quality. At each user terminal, a virtual space with a plurality of regions defined therein in correspondence to a plurality of multicast groups is displayed on a screen, while an information indicating a range of each region in the virtual space is stored in correspondence to an address information for a corresponding multicast group. A desired position in the virtual space on the screen is specified by an input device, and joining/leaving to/from multicast groups is controlled by using the address information stored in correspondence to a region in the virtual space which contains the desired position. The display on the screen may include a plurality of zones defined within each region in correspondence to a plurality of different communication qualities, so that a communication quality of a multicast communication to be received can be controlled according to a zone within a region in the virtual space which contains the desired position.