PURPOSE: To forecast fault generation and to deal with abnormality before the fault generation by updating data in a protecting operation processing time storage means each time protecting operation processing is generated corresponding to abnormality before the fault generation, and informing a main controller of that the number of times for protecting operation processing reaches the reference number of times for protecting operation processing.

CONSTITUTION: A main storage means 3 is provided with plural areas for storing the plural sets of the same data, a main control part 2 checks data and when data are rewritten or broken, data in a normal area are written in an area, where the data are rewritten so as to maintain data. Then, an arithmetic control part 4 adds '1' to data showing the number of times generating the protecting operation processing stored in a protecting operation processing time storage means 5 and when this value is smaller than the reference number of times generating the protecting operation processing stored in a reference protecting operation processing time storage means 6, the added data are stored in the protecting operation processing time storage means 5. When the value is larger, the main control part 2 is informed thereof and processing such as increasing the storage area of data is performed so as to prevent the fault generation by breaking all the data.