An abnormality detection unit according to the invention includes a processor, and a light source device configured to emit light for each of segment periods that are time divided within a frame, and the processor obtains an illuminance value of light emitted into the frame from the light source device after a predetermined delay time has elapsed, whereupon a segment period results where a highest illuminance value is obtained, from a timing of receiving a trigger signal that is in synchronism with the frame, and detects that the light source device is in an abnormal state, when the illuminance value is less than a predetermined threshold.