A method of detecting knocking intensity of an internal combustion engine uses a detector for detecting vibration propagated within the engine and a first calculation circuit for obtaining an average value of vibration sensed by the vibration detector within a predetermined crank angle before the top dead center, and in which knocking is identified when the ratio between the above average value and the maximum value of vibration after the top dead center exceeds a predetermined value. This method also uses a second calculation circuit for obtaining a further average value of vibration detected by the vibration detector within a predetermined crank angle after the top dead center of the internal combustion engine, and a knocking discrimination circuit for generating a knocking indication output corresponding to the ratio between the average value of vibration before the top dead center obtained by said first calculation circuit and the average value of vibration after the top dead center by said second calculation circuit.