PURPOSE: To exactly prevent an erroneous data from being written, by adding the discriminating information to data respectively in each data holding device, collating these discriminating information, and confirming whether each data in each data holding device is in a correct relation or not.

CONSTITUTION: A data discriminating code is added in advance to each data in a floppy disk device 14 (or a magnetic tape unit 15) and a key card KC, prior to read and write of a data, these data discriminating codes are read out and collated. Subsequently, whether each data in the floppy disk device 14 (or the magnetic tape unit 15) and the key card KC is in a correct relation or not is confirmed, and when it is confirmed that each data is in a correct relation, read and write of a data by a read/write control part 39 are executed. In such a way, write of an erroneous data can be prevented exactly.