PURPOSE: To succeed to the unchanged contents of a back-up memory after the contents are changed by converting the logical form with the use of a logical form recognizer stored in the back-up memory.

CONSTITUTION: A logical form recognizing part 1 reads a logical form recognizer out of a back-up memory 4 in an ON state of a power supply and recognizes the logical form of the memory 4. A conversion processing part 2 reads the contents of the memory 4 based on the logical form informed from the part 1 and then writes the contents into the memory 4 again after converting them into a logical form to be activated at present. In such a way, the logical form of the memory 4 is recognized in an ON state of the power supply and then converted. Thus it is possible to succeed to the unchanged contents of the memory 4 after these contents are changed when the logical form of the memory 4 is changed.