In an ignition device, a base section of a discharge chamber is formed by a part of a central dielectric body. A front section of a ground electrode and a front end section of the central dielectric body are projected toward a combustion chamber of a head cylinder of an internal combustion engine by a predetermined height which is measured from a top ceiling wall of the head cylinder. The predetermined height of the front end section of the central dielectric body projected into the inside of the head cylinder is the same or higher than the predetermined height of the front end section of the ground electrode projected into the inside of the head cylinder. The predetermined height of the front end section of the ground electrode is within a range of 3 mm to 25 mm.