Ignition device for internal combustion engine

An ignition device for an internal combustion engine comprising:

• an ignition coil comprising a primary winding and a, secondary winding, the ignition coil generating an igniting high voltage in the secondary winding by turning off a primary current flowing in the primary winding;
• an ignition switching unit for turning on/off the primary current;
• a spark plug connected to an igniting high voltage generation end of the secondary winding for generating a spark discharge between electrodes of the spark plug in a condition that a discharge current generated on a basis of the igniting high voltage flows in the spark plug;
• a reverse current prevention unit series-connected on a current-conduction path of the discharge current connecting the secondary winding to the spark plug, the reverse current prevention unit permitting conduction of the discharge current in the spark plug but preventing conduction of a current generated in the secondary winding at a time of carrying a current to the primary winding;
• a voltage application unit connected to an other end of the secondary winding opposite to the igniting high voltage generation end for applying an ionic current-detecting voltage to the spark plug, the ionic current-detecting voltage being identical in polarity to the igniting high voltage applied to the spark plug;
• an ionic current detection unit for detecting an ionic current flowing in between the electrodes on a basis of application of the ionic current-detecting voltage;
• and
• an ionic current detection switching unit series-connected on a current-conduction path of the ionic current-detecting voltage connecting the voltage application unit to the other end for making the current-conduction path non-conductive to apply the ionic current-detecting voltage at a time of generation of the igniting high voltage but making the current-conduction path conductive to apply the ionic current-detecting voltage at a time of detection of the ionic current on a basis of external commands.