PURPOSE: To obtain a spark advance amount suitable for the load for an engine with a simple circuit, by connecting a variable resistor in parallel with a capacitor which is adapted to differentiate the positive half-wave of the output of a pulser coil, and by controlling the value of the resistor in accordance with variations in the load of the engine.

CONSTITUTION: A capacitor discharged type ignition circuit 10 is constituted such that a capacitor 16 is charged with the current which is obtained by making the alternate output of a charging coil 12 to be subjected to half-wave rectification, and is discharged when a thyristor 18 is energized at a predetermined ignition time. A spark plug 22 generates sparks due to a high voltage which is induced in the secondary side part of an ignition coil 20 upon the above-mentioned discharging. The thyristor 18 is energized by the output of an idle spark advance circuit 26 or a main spark advance circuit 36 which are selectively used by switching a speed detecting switch 46. In this case, the main spark advance circut 36 comprises a diode 38 for carrying out half-wave rectification to the alternate output of a pulser coil 25, a parallel circuit of a differentiating capacitor 42 and a variable resistor 44, etc. The variable resistor 44 is associated with the open and close operations of a restrictor valve.