There is provided a leakage detection apparatus that can accurately detect a leakage condition in an internal combustion engine having a cylinder resting function. An ignition plug provided in the combustion chamber of a cylinder is made to generate an ignition signal at least once when based on an instruction from a cylinder resting control unit, a fuel injection valve and a valve driving mechanism are stopping the operation thereof; the leakage condition of the ignition plug is detected based on an output signal generated by an ion current detection circuit at a timing other than the timing when ignition discharge is caused.