PURPOSE: To process assuredly a microprogram within a fixed time by comparing the time needed for the processing not required urgent execution with the remaining time after the execution of the processing required urgent execution.

CONSTITUTION: A counter circuit 1 and FF40W4m are reset via a signal line l2 before the processing required urgent execution. The circuit 1 is counted up as the processing not required urgent execution, and the executing steps of a program are counted. When the count-up operation is repeated, some of comparators 30W3m have the input value of an input terminal A larger than that of an input terminal B. Thus the corresponding FF40W4m are set and logic 1 is properly outputted to output lines l30Wl3m respectively. In addition, the outputs of FF40W4m showing the result of comparison with the value that is smaller than and most approximate to the number of steps needed for the processing not required urgent execution are tested before the execution of said processing. In case no output is set, the processing not required urgent execution is executed.