PURPOSE: To achieve the stable operation by providing a primary current control switch to be applied with different control signal in accordance to the operating state thereby suppressing the variation of the firing position under low speed while making the firing position fixable to the maximum lead angle position in predetermined region of high speed region.

CONSTITUTION: A signal coil 23 for sequentially producing negative and positive half cycle signals for every rotation of an engine is provided in a firing position controller 20 for cntrolling the firing position in accordance to the rotation of the engine, and the positive half cycle signal is provided as the primary current control switch or the thyristor 3. Furthermore a signal supply circuit comprised of a resistor 25 and a diode 26 for providing another control signal to the thyristor 3 is provided where one end 25a of the resistor 25 is connected to the collector of a signal supply control semiconductor switch or a transistor 27. Both of said control signals are selectively applied to the thyristor 3 in accordance to the output of comparator circuits 43, 49 on the basis of the terminal voltage of capacitors 31, 32.