In an ignition plug, since a ground electrode is formed in a thin-rod-shape or a mesh-like shape, sufficiently strong radicals are locally generated by a barrier discharge, an anti-inflammation effect by the electrode is small, and the growth of a flame is hardly hindered. Furthermore, by making the thickness dimension of a second dielectric facing a discharge region uniform, the barrier discharge is spread over the surface of the second dielectric, the generation of the radicals is maintained, and combustibility after ignition is promoted. Furthermore, because an end portion of a high voltage electrode and a ground electrode are disposed to face each other within a combustion chamber, a fuel gas introduced into the combustion chamber is liable to flow into the discharge region, and is easily ignited by the radicals generated due to the discharge.