To enhance a data transmission efficiency by sending different kinds of mixed data without acquiring confirmation from an opposite station so as to utilize effectively a time slot.

A transmission data changeover section 103 reads transmission data in a voice data processing section 905 or a non-voice data processing section 906 according to a command from a mode changeover control section 105 and sends the data to a changeover instruction additional section 104. Furthermore, a transition type decision section 108 discriminates whether or not a data amount to be sent by the processing section 905 or 906 exceeds a predetermined data amount, and when in excess, a confirmation type mode changeover control section 106 is operated and when not in excess, a non- confirmation type mode changeover control section 107 is operated. The control section 107 allows a transmission section 901 to send non-confirmation type mode changeover instruction non-voice data (data arranged dividedly to two time slot channels, and non-confirmation type mode changeover instruction is arranged in a control channel of each time slot).