PURPOSE: To shorten the time necessary to detect a data error at a receiving side by adding a prescribed code to the peak side of data to be transmitted, transmitting it from a transmitting side, decoding a prescribed received code and detecting the transmission error of the transmission data by the result.

CONSTITUTION: A prescribed code 1b is added and transmitted to the peak side of data 1a to be transmitted and at the receiving side, the prescribed received code 1b is decoded. Thus, since it is obvious whether or not an error occurs at the data received at a receiving part, when an error detecting code is received, the re-transmission can be immediately executed at the time point without awaiting the receiving completion of all data and the processing time necessary to the re-transmission at the time of generating an error is shortened.