Misfiring detection apparatus for internal combustion engine

In a misfiring detection apparatus according to an embodiment, a comparison unit 22 and a time counting unit 24 accumulate periods of time during which the ion current flowing between the center electrode 10a and the ground electrode 10b of a spark plug 10 exceeds a predetermined current value; and an ECU 26 judges that misfiring has occurred when a total of the accumulated periods is not greater than a predetermined value. Thus, the ion current can be grasped as a cumulative value of generation periods of the ion current. Therefore, even when the ion current contains a discharge noise component, the discharge noise component having a short duration accounts for only a small portion of the cumulative value, so that influence of the discharge noise component can be reduced. Accordingly, detection of misfiring can be performed with improved accuracy.