Internal-combustion-engine ignition diagnosis apparatus

An ignition diagnosis apparatus for an internal combustion engine in which an inflammable fuel-air mixture taken in by a combustion chamber of a cylinder is ignited to burn by a plurality of ignition devices, the internal-combustion-engine ignition diagnosis apparatus comprising:

• an ion detection device that is provided in at least one of the plurality of ignition devices and detects an electric quantity based on an ion produced in the combustion chamber due to combustion of the inflammable fuel-air mixture;
• an ion occurring timing detection device that detects an ion occurring timing, based on the electric quantity detected in a predetermined detection period;
• and
• an ignition abnormality determination device that compares the detected ion occurring timing with a comparison timing set in such a way as to be delayed in terms of the rotation angle of a crankshaft of the internal combustion engine with respect to an ignition timing set for the ignition device provided with the ion detection device, and determines that ignition performed by the ignition device provided with the ion detection device is abnormal, in the case where the ion occurring timing is delayed in terms of the rotation angle of the crankshaft with respect to the comparison timing.