An external electrode lamp (2) comprises a glass discharge vessel (4) in which a discharge medium is sealed and first and second electrodes (6, 8) provided outside the discharge vessel. Since the area of the first external electrode is larger than that of the second one, the capacitance of a first capacitor composed of the first external electrode and a first dielectric section including a portion of the discharge vessel between the first external electrode and the discharge medium is larger than that of a second capacitor composed of the second external electrode and a portion of the discharge vessel between the second external electrode and the discharge medium. As a result, if the high-voltage output of the starting circuit is connected to the first external electrode, the second external electrode is grounded, and a voltage is applied, the voltage to ground at the portion facing the first external electrode of the inner wall of the discharge vessel is higher than conventional, and the discharge can be easily started, thus improving the dark startability.