An electrodeless discharge lamp operating device including an electrodeless discharge lamp 3 and a ballast circuit 4, wherein the ballast circuit 4 includes: an AC-DC converter 5 for converting a phase-controlled AC voltage into a DC voltage; a DC-AC converter 6 formed so as to intermittently drive the electrodeless discharge lamp 3 due to the existence of an operating period during which a high-frequency voltage is applied to the electrodeless discharge lamp 3 so that the electrodeless discharge lamp 3 is operated, and an extinguishing period during which the generation of the high-frequency voltage is stopped so that the electrodeless discharge lamp 3 is extinguished; and a dimming controller 7 for detecting the turn-on of the phase-controlled AC voltage, for outputting an intermittent command signal that changes the ratio between the operating period and the extinguishing period to the DC-AC converter 6, and for outputting a signal that maintains an intermittent dimmable operating state even if dimming state is in full illumination.