PURPOSE: To decrease the transmission errors by defining the memory contents change answer data on a remote device as the detection data to the contents of the data to be changed.

CONSTITUTION: When the memory contents change instruction data 1 is inputted to a memory contents change request data editing part 2, the part 2 edits the memory contents change request data to output this to a communication part 5 of a computer. Then a 1st error detection code is calculated to a cyclic code checking code, etc., by a prescribed calculation method against the memory contents change request data. the calculated error detection code is stored in an error detection code store part 3. The memory contents change request data sent to a communication part 6 of a remote device from the part 5 via a data transmission circuit 11 is interpreted by a memory contents change process part. A memory contents change answer data editing part 8 produces a 2nd error detection code in an error detection code production job area 10 against a changed memory 9 to be changed and outputs the produced detection code to the part 6 of the remote device. Thus it is possible to confirm whether the memory of the remote device is correctly changed or not.