PURPOSE: To reduce the communication time and to improve the communication efficiency by interrupting the communication only when an error is detected in a reception data.

CONSTITUTION: A reception counter is set every time a data is received and should an error be detected in a reception data shown in (A), an error flag B at a reception side is set to 1 as shown in (C), and the count by a reception counter is started. Moreover, two kinds of error flags are prepared in this way. The one is an error flag A which is set through the detection of an error and reset before error correction processing to make a succeeding data receptible, and the other is the error flag B which is kept set after an error is detected till the error correction is finished. In this case, after a data D as shown in (D) is sent corresponding to the reception data and the transmission is interrupted for a prescribed period T3 only. Thus, the reception of the opposite party is interrupted, the transmission by this interruption is interrupted for a prescribed period and the error is corrected by utilizing the period.