An ignition apparatus for an internal combustion engine is capable of avoiding mis-ignition even if subject to external disturbances when a fail signal is transmitted through a common signal line on which an ignition signal can also be transmitted. An igniter is connected to receive the ignition signal from an ECU, and includes a waveform shaper connected with the signal line and having an input connected in parallel to an input resistance so as to make a voltage at the input higher than a prescribed voltage when the ignition signal flows into the input resistance, and a pulse output circuit connected to the input and having an output for generating the fail signal into which a secondary coil current is converted. The pulse output circuit adjusts a fail signal current such that the voltage at the input when the fail signal flows into the input resistance becomes less than the prescribed voltage.