Engine spark timing controlling device

An engine ignition timing controlling device for an engine having a plurality of cylinders comprising a resonant type vibration sensor for detecting the knocking level of an engine and having a resonant frequency which is within the knocking frequency range of said engine, a means for detecting the mean vibrational level of the engine, means for sampling a peak value of an output signal of the sensor for a period of time which is inversely proportional to the engine speed and holding the sampled peak value until an ignition time for the next cylinder is reached, a means for comparing the mean vibrational level detected by said detecting means with said peak value sampled by said sampling and holding means, a means for generating an ignition standard signal corresponding to a driving condition of the engine, a means for determining a retardation angle of ignition timing with respect to the ignition standard signal in accordance with an output signal of the comparing means, a means for generating an ignition timing signal based on the output signal of the determining means, wherein retardation angle of ignition timing with respect to said ignition standard signal is controlled when knocking occurs to optimize the knocking of the engine.