In a light source device in which one or more light emitting tubes are adapted to emit light sequentially, there are provided one or more counters for counting the number of times of failure of light emission of the light emitting tubes, and comparator or judging circuit for comparing the number counted by the counters with a predetermined number to produce an interruption signal when the counted number is over the predetermined value, a control unit acts to interrupt the light emission of the light emitting tube in response to the interruption signal and a warning device is activated for indicating a warning in response to the interruption signal.