An ignition device for an internal combustion engine including: an exciter coil that generates an AC voltage having a positive half wave and first and second negative half waves generated before and after the positive half wave with rotation of the internal combustion engine; and an ignition control portion that controls an ignition position of the engine using a microprocessor to which a power supply voltage is supplied from a power supply circuit that converts the voltage having the negative half waves generated by the exciter coil to a DC voltage, wherein the ignition control portion is comprised so as to cause a timer to start a counting operation at the start of the operation of the microprocessor, regard a measurement value of the timer as time between generation of the first negative half wave and generation of the second negative half wave to arithmetically operate counting data for measuring the ignition position based on rotational speed information of the engine obtained from the time, and immediately measure the arithmetically operated counting data to generate an ignition signal.