knock detection device for an internal combustion engine

Device for knocking detection for an internal combustion engine having a knock pulse signal bit noisy even if the detected ion current varies with the type of fuel or candles: a vibratory component superimposed ion current produced by the combustion fuel is extracted and set pulse waveform by comparison with a threshold value, the number of pulses is calculated by a calculation unit, and an ignition timing control being effected on the basis of the calculation. An integration circuit (23) includes (charge) the vibratory component and a discharge circuit (24) discharges a predetermined amount of charge from the integrated charge. The threshold value (Th1) is self-regulated by a balance between charge and discharge the integrating circuit (23) and the discharge circuit (24).