In a mobile telephone terminal at the transmitting end, voice data to be transmitted are sequentially inputted, and it is determined whether the inputted voice data are silent. The voice data regarded as silent voice are replaced by group numbers, while the voice data indicative of sonant voice as well as the group numbers as replaced are transmitted by wireless. On the other hand, in a mobile telephone terminal at the receiving end, the signals transmitted by wireless are received, and the voice data and group numbers of the received signals are discriminated. The voice data are reproduced as they are, while the group numbers are reproduced as silent, and further processings based on the group numbers are executed. This allows predetermined data to be repetitively transmitted with a high efficiency without degrading communication quality very much. This also facilitates a follow-up participation in a group call.