PURPOSE: To intentionally perform repairing or replacement under sufficient investigation by detecting and judging operation defficiencies by continuously monitoring the data from various sensors and a drive mechanism and changing over operation to a bypass circuit when repairing is judged to be possible to continue operation.

CONSTITUTION: An control unit 13 inputs the analogue signals from a drive mechanism 14 and various sensors 15 not only to store them in a memory device 16 but also to output them to a display device 17. The control unit 13 compares the input signals with the data at the time of normal operation taken in the memory device 16 and outputs a control signal to the drive mechanism 14 while monitoring abnormality. Further, in this continuous monitor, the operation deficiencies of a part or a mechanism are detected and judged and, at the same time, it is diagnosed whether or not a deficient state can be repaired. When the control unit 13 judges that the deficient state can be repaired, a signal changing over operation to a bypass circuit 18 having a preparatory part or mechanism arranged thereto is outputted to continue the operation due to the bypass circuit 18.