PURPOSE: To prevent line occupied time accompanied by means of the transmission of transmission information from being prolonged by automatically converting a character code included in transmission information into image data so as to transmit it when a retransmission request for transmission information including the character code from a reception side exceeds the prescribed number of times.

CONSTITUTION: When an error is detected in the reception-side, the reception-side transmits a retransmission request signal to a transmission side until the reception-side receives accurate transmission information. When a retransmission request signal detection part 113 on a transmission side detects a retransmission request signal from the reception side, a counting part 114 counts the number of the retransmission request times and effect that there is the retransmission request is informed to a system control part 115. The system control part 115 obtains the count value of the counting part 114, judges whether the count value exceeds the previously set number of times or not. When the retransmission request exceeds the prescribed number of times, the character code included in communication information is automatically converted into image data and it is transmitted. Thus, a line is prevented from being occupied for a long time even if the circuit state of the transmission line is deteriorated.