Abstract: A device for detecting knocking in an internal combustion engine capable of preventing noise caused by unstable combustion from being erroneously discriminated as the occurrence of knocking. An integrated value of ionic current detected by an ionic current detecting unit 19 is supplied to an ignition timing control unit 14 through an LC resonance masking unit 31, a band-pass filtering unit 32 and an integrating unit 33. A timeaverage of the integrated values is determined as a background, and it is determined that knocking is occurring when the integrated value becomes larger than a product of a predetermined coefficient and the background (BG). Further, an average of BG is learned as a BG learning value of WOT. When BG is larger than the learned BG during the low-load operation, it is determined that the combustion is unstable, and a predetermined coefficient is increased to prevent the occurrence of erroneous discrimination.