Abstract: According to this invention, a limited multicast communication notice indicating that an identical message is transmitted to a plurality of arbitrarily designated stations is transmitted prior to transmission of a text message. The notice includes definition data. The notice is received by a data input/output section, and it is checked by a comparator if the notice is a message destined to be sent to the intrastation. If it is discriminated that the notice is destined to be sent to the intrastation, the notice is received, and the definition data in the notice is held in the comparator. Thereafter, a CPU forms a response message and sends it to a source station. Thereafter, a text message is transmitted using limited multicast transmission. It is checked by the comparator if the received message includes the same definition data held in the comparator. As a result, if the received message includes the definition data, the message is received by the serial input/output section and is stored therein.