PURPOSE: To unnecessitate a deviation calculating circuit that has been required in the conventional system, by making comparison between a signal representing an aimed injection timing and a signal representing the actual injection timing, and enabling to control the injection timing correctly by simply obtaining the result of the above comparison as a binary signal.

CONSTITUTION: An injection timing controlling system of this invention comprises a rotation detector 2 for producing a rotation signal N relating to the revolutional speed of an internal combustion engine and a sensor 3 for producing a load signal L representing the load acted to the engine and a water-temperature signal W representing the temperature of engine. These signals N, L, W are outputted to an aimed signal generating circuit 4. An aimed injection timing signal S1 obtained in the circuit 4 is impressed to one input terminal of a comparator 5 and compared with an actual injection timing signal S2 given from a detector 6 to the other input terminal of the comparator 5. A judgement signal S3 of a binary signal is given to a driving circuit 7, which produces a drive signal S4 and impresses the same to a hydraulic timer 8. Here, the timer 4 operates to open a solenoid valve and to advance the ignition timing when the drive signal S4 takes a high level.