To reduce the number of part items so as to form a circuit with ease and a low cost.

In an internal combustion engine in which the output of the power generating coil 1 of an ignition power supply generated by an engine rotational speed, is made to accumulate in a capacitor 3, and this accumulated charge is released to an ignition coil 4 through a control element 6 operated by an ignition signal corresponding to the engine rotational speed so as to generate spark in an ignition plug 5, a low pass filter 9 by which the ignition signal is made to be set at an ignition threshold value or below so as to be inputted into the control element 6 when the engine rotational speed becomes a predetermined value or more, is arranged so that the control element 6 becomes inoperative so a to prevent spark from being generated in the ignition plug 5.