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It is well known that the wavelet transform is a useful time-frequency analysis method for an unsteady signal and major attention has been focused on the selection of the mother wavelet (MW) because the MW plays an important role in the wavelet transform. In this study, we analyze the pressure signal in a spark-ignition engine and the vibration of the engine block measured by a knock sensor under the knocking conditions when knocking is caused. We then propose a new method of the knocking detection that utilizes the knocking signal measured with a knock sensor as a MW. We call this method the Instantaneous Correlation Method (ICM). The degree of similarity between the MW and the vibration of the engine block was judged and only the knocking signal from the vibration of the engine block was extracted. The results obtained here show that the method proposed in this study is useful for knocking detection even if the engine speed is very high of 6000rpm.