A network composed of a primary segment, in which a management server, a primary distribution server, and a data storage server are disposed, and a secondary segment, in which a plurality of targets connected to the primary segment via a router which does not support multicast, serves as an object. When a multicast distribution request is received at the management server, a secondary distribution server is temporarily built and operated on a particular target of the secondary segment, data is transmitted by unicast from the data storage server to the secondary distribution server via the router, and the data is transmitted by multicast from the secondary distribution server to the targets on the same segment.