An ignition plug includes an insulator having an axial bore extending in the direction of an axis and an electrode inserted into the axial bore, and generates plasma discharge through supply, to the electrode, of high-frequency power generated by a predetermined high-frequency power supply. The electrode includes a center electrode inserted into the forward side of the axial bore and a terminal electrode inserted into the rear side of the axial bore. In the axial bore, the terminal electrode and the center electrode are fixed to the insulator by means of a glass seal which contains a glass component, and are in direct contact with each other. Thus, ignition performance can be further improved.