A device for detecting knocking in an internal combustion engine which, when spike noise or noise due to disturbance in the flame in low-load running are generated, does not erroneously detect it as knocking. Knocking frequency components passing through a band-pass filter 32 and frequency components lower than the knocking frequency and passing through a low-load noise band-pass filter 321 are picked from the ionic current detected by an ionic current detecting unit 17. When the level of the low-frequency components is larger than a predetermined value, it is regarded that the noise is generated due to unstable combustion during the low-load operation or the spike noise is generated due to corona discharge of a spark plug 16, and the determination of the occurrence of knocking is prevented. This constitution makes it possible to prevent erroneous detection of knocking.