Abstract: A generation-stop detection system of an alternator is provided. A unit provides a generation-stop condition signal when an output voltage of the alternator is lower than a reference voltage. A rotation speed detection unit detects a rotation speed. A reference voltage changing unit changes the reference voltage proportionally to the rotation speed of the alternator. A warning signal unit provides a warning signal if the generation-stop condition signal is provided at a rotation speed lower than a predetermined speed. The warning signal is maintained even when the rotation speed of the alternator becomes higher than the predetermined speed. The warning signal is interrupted when the output voltage of the alternator is higher than the voltage of the battery.