PURPOSE: To enable a microprogram controller to detect its own abnormality and display the result to outside by itself by providing a run monitoring function to monitor the abnormal run of the microprogram of the microprogram controller.

CONSTITUTION: A microprogram controller 1 is provided with a microprocessor 10, a control storage 11, a specific address detecting circuit 20, a time monitor circuit 21 and a time-out display circuit 22. The circuit 20 outputs a specific address detecting signal 200 every time when a specific address showing the run of an idle routine is detected out of an internal bus 100. The circuit 21 starts a monitor timer for each supply of the signal 200 and outputs a time-out signal 210 when the monitor timer counts its set time. Then the circuit 22 holds the signal 210 and also displays the holding state of the signal 210.