PURPOSE: To finish an appropriate self-diagnostic program dealing with a time difference in the shortest time by calculating the time difference between an off-time and a stored on-time when the on-time is detected and selecting and executing any one of self-diagnostic processing programs among the self- diagnostic processing storing means in accordance with the time difference.

CONSTITUTION: A control part 11 requires a time measuring part 12 to read out the time data stored by a time storing memory 14. The time data is set in the reduction register of a calculation part 15. Next, the control part 11 requires the time measuring part 12 to read out the present time. The read-out time data is set in the minuend register of the calculation part 15 by the control part 11 so as to read out reduction results. The numerical value is regarded as the off-time. Next, the off-time is inputted by the control part 11 to a comparator 17 so as to obtain the address of a corresponding self-diagnostic processing memory 16. Then, any one pf the self-diagnostic processing programs is executed based on the obtained address.