PURPOSE: To easily and quickly execute a processing of an error, when an error has been generated in a data, by transferring periodically the same data until a new data is generated, when a data to be transferred newly does not exist at the time of transferring a data.

CONSTITUTION: In case of a transferring a data between a local area network LAN 10 and an electronic computer 20, it is executed through a private line 31 for transmission of a gateway GW 11 and reception of a communication interface IF 21, and a private line 32 for transmission of the IF 21 and reception of the GW 11, as for the GW 11 and the IF 21. The GE 11 and the IF 21 transfer periodically the data even if an error is generated in the course of transferring the data, respectively, and when the transmission side has no new data, the data which has been transferred immediately before it is transferred as it is. Also, when the reception side receives no data for a prescribed time, it is decided that the transmission side is abnormal, and also, when the data whose data format or parity is different has been received continuously by a prescribed number of times, it is decided that the transmission side is abnormal. Even when an abnormality has been generated in the received data transfer, it is unnecessary to executed a complicated processing by receiving the next data.