A first storage unit stores a reception count, which is the number of simultaneously-occurring messages for each of subscribers corresponding to subscriber identification information. A second storage unit stores a predetermined number of the simultaneously-occurring messages, which is an upper limit of allowing the messages to occur in parallel, for each of the subscribers corresponding to the subscriber identification information. A third storage unit stores each message identification information corresponding to each of the simultaneously-occurring messages, together with the order of occurrence, for each of the subscribers corresponding to the subscriber identification information. A control unit controls transfers of the simultaneously-occurring messages, by controlling the first, second, and third storage means according to the transfer order identification information, the subscriber identification information, and the message identification information extracted from the received data unit.