An electrodeless lamp protecting device installed between an electrodeless lamp and a power source comprises a substrate having a feedback signal input module, a signal level determination module and a protection signal output module installed on the substrate. A signal of the power source is transmitted from the feedback signal input module to the signal level determination module, and the signal serves as a reference for an output signal of the protection signal output module, such that the electrodeless lamp has an automatic protection function upon the receipt of an abnormal signal.