A control device for an internal combustion engine comprising: a knocking sensor for detecting a knocking signal of the internal combustion engine; a band pass filter for extracting a knocking signal of a predetermined frequency band from the output signal of the knocking sensor; a high pass filter comprising a capacitor and a resistor for extracting an AC component from the output of the band pass filter; a rectifying circuit having a one-way conducting element and a resistor for achieving positive half waves from the AC output of the high pass filter; and a peak hold circuit for detecting a peak value from positive half wave pulses output from the rectifying circuit, holding the peak value for a predetermined time and outputting the peak value to ignition timing control, wherein the one-way conducting element of the rectifying circuit is constructed as a negative voltage clipping mechanism for achieving positive half waves by short-circuiting negative half waves, and also with respect to each of the circuit elements constituting the high pass filter and the rectifying circuit, each constant thereof is set so that the charging time constant and the discharging time constant to the capacitor are equal to each other.