An ignition device includes a spark plug and an ignition coil. The spark plug is attached to a cylinder head such that a center electrode and a ground electrode project into a combustion chamber. In an internal combustion engine, airflow is generated in a predetermined direction to the spark plug during a compression step. The ignition coil has a primary coil and a secondary coil. An output voltage of the secondary coil after interruption of energization of the primary coil is restricted to a predetermined voltage or less. The ground electrode has a leg portion extending from a housing of the spark plug and an opposing portion that extends in a direction intersecting with the leg portion and forms a gap by opposing the center electrode. The leg portion is attached to a position further upstream than the gap in a flow direction of the airflow during the compression step.