An ignition apparatus includes an ignition plug, a boost transformer, an ignition power source and a measurement unit. The ignition plug has a center electrode and a ground electrode. The boost transformer supplies the ignition plug with electric power generated in a secondary coil upon supply of AC power from the ignition power source to a primary coil. The measurement unit measures the discharge voltage of the ignition plug. The ignition power source includes a discharge state determining unit that determines the discharge state of the ignition plug based on the measured discharge voltage and a current controlling unit that controls electric current supplied to the primary coil. When a discharge path formed between the center and ground electrodes of the ignition plug is determined by the discharge state determining unit as being in an over-extended state, the current controlling unit reduces the electric current supplied to the primary coil.