An ignition device of an engine includes a control unit and an igniter including an ignition coil having a primary and a secondary winding. Supply and stop of a current to the primary winding are performed based on the ignition signal to generate high voltage in the secondary winding thereby to cause a spark to a spark plug provided for a cylinder of the engine. The control unit includes an engine speed variation detector that detects an engine speed variation. The control unit determines a misfire occurs in the cylinder when the engine speed variation is at or higher than a first threshold and smaller than a second threshold that is greater than the first threshold. The control unit determines an abnormality occurs in the igniter in the cylinder when the engine speed variation is at or higher than the second threshold.