over by judging the state in which a false normal state is likely to occur by estimating pre ignition which is another cause of serious trouble in reciprocating engines according to the safety control apparatus for an internal combustion engine of the second embodiment therefore it is possible to prevent in advance serious trouble in which pistons are melted and the engine is damaged by the occurrence of pre ignition that stems from an increase in the advance of the ignition timing of the engine according to the second embodiment the hold circuits 81a to 81h are provided in the paths of ignition control signals from the control unit in the first control system a and the control system is changed over when an abnormality in the ignition timing is detected by the window producing circuit 80 it is however also possible to change over the engine control system by providing an ignition timing detection means separately from the passages of ignition control signals and by controlling the control unit observation circuit relying upon the detection output in this case furthermore the ignition timing detection means can also be realized by using the software in the other control unit i e in the second control unit 72 according to the second embodiment furthermore the hold circuits 81a to 81h are provided in only the paths of ignition control signals from the control unit in the first control system a and the control.