PURPOSE: To diagnose the state of a control part without mounting mechanical parts, by providing a means for detecting the signal from the outside, a means receiving the signal of said means to perform the self-diagnosis of a control part and a means for displaying the diagnostic result of said means.

CONSTITUTION: When the signal from the outside is detected by a signal detection part 1, processing is transferred to a control part diagnosing processing part 2. Herein, the diagnosis of ROM6, RAM7 or peripheral LSI4 is performed and, in an apparatus using a plurality of CPUs, the self-diagnosis of other CPU is performed. When abnormality is discovered on the way of diagnosis or when all of diagnostic operations are normally finished, the control part diagnosing processing part 2 transmits diagnostic results to an operator through a diagnostic result display part 3. The diagnostic result display part 3 performs display by LED or a buzzer. Therefore, the state of a control part can be diagnosed without mounting mechanical parts.