Abstract: An abnormality detector for a light source includes a laser diode which emits an excitation light and a fluorescent substance which is excited by the excitation light to generate a fluorescent light. The abnormality detector includes a first photo sensor which is sensitive to a wavelength of the excitation light, a second photo sensor which is sensitive to a wavelength of the fluorescent light, a first current-voltage conversion circuit which outputs a first detection signal based on an output of the first photo sensor, a second current-voltage conversion circuit which outputs a second detection signal based on an output of the second photo sensor, and a determination unit which determines whether an abnormality occurs based on the first detection signal and the second detection signal.