PURPOSE: To keep reliability without generating the delay of a line by returning a code signal when an error is generated at the time of receiving data modulat ed and transmitted together with image information while adding a line number for each line, and performing control so as not to send the data again in the case of retransmission when the error amount is less than a prescribed amount.

CONSTITUTION: On the transmitter side, the information of an original is read, and the line number encoding the data by an encoder 16 is added for each line, modulated by a modulator 24 and sent together with the image information. On the other hand, on the receiver side, this line information is properly received, in the case of signal detection 44, the code signal is removed, and the data are decoded by a decoder 60. Further, when this line information is erroneously received and detected 44, code information corresponding to the line information is returned to the transmitter side and the retransmission of line information is requested. In this case, when the error reception amount less than the prescribed amount is detected 44, the information is recorded 64, and the retransmission is not requested. Thus, the reliability of the line can be held without delaying the line.