step s 13 thus the electric current to the ignition coil of the ignition system 21 will be stopped in accordance with the ignition instruction from the cpu 6 causing the spark plug to generate a spark therefore when it has been detected that the engine speed ne is within the range of n1 u2266 ne lt 2 and the transmission gear ratio is high the engine is running under a condition where knocking occurs in this case the ignition timing is retarded to retard spark arcing at the spark plug by the amount of ignition retardation ingk set at step s 7 in the above described embodiment a single cylinder internal combustion engine has been described but the present invention is not limited thereto and is applicable to a multi cylinder internal combustion engine it should be noted that the ignition timer stated above is formed by a program and may be formed of hardware furthermore when the throttle valve opening or the amount of change in the opening is under the specific value it is possible to not retard the ignition timing according to the ignition timing control apparatus of the present invention as heretofore described when it has been detected that the engine speed is within a specific speed range and the transmission gear ratio is high the engine is determined to be under a condition where knocking is likely to occur therefore the ignition timing of the internal combustion engine can be retarded under a knocking condition the ignition timing is instantly retarded to generate a spark.