PURPOSE: To record the diagnostic information and to refer to this information for diagnosis of the next same fault by incorporating a self-diagnostic recording medium into a control panel containing an NC device, a display device, etc., and diagnosing the situations under the guidance of the display device.

CONSTITUTION: An NC device 2 which performs the numerical control and a sequencer 3 which performs the sequence control are connected to a machine tool 9 via an interface 1. A control panel 4 provided with a CRT, i.e., a display device is connected to the device 2, and an operator inputs the information to the panel 4. Then the panel 4 operates the tool 9 and the device 2 and also performs the display through the device 2 and the sequencer 3. In a diagnostic mode, a self-diagnostic program is independently driven by a self-diagnostic controller 6. Thus the faults are diagnosed based on the information received from the device 2, the sequencer 3 and the panel 4 together with the inference carried out based on the data recorded on a card 7.