PURPOSE: To diagnose properly a lighting device by converting an output of a photosensor array input video signal data, representing a lighting output profile and discriminating whether or not the signal is within a designated calibration value which has been set in advance. CONSTITUTION: A scanning driver 80 moves a lamp 25 until it comes directly below a calibration strip reflecting piece 84, the lamp 25 is lighted, and a profile of a luminous quantity of the lighting device is sampled within a predetermined time interval selected on a screen. The reflected light of the reflecting piece 84 is given to an array 24 via a lens 28, and an output of the array 24 is fed to an AGC circuit, converted into a digital signal, and is fed to a processor. The processor converts this signal into a signal for display with a histogram bar. Thus, the sample profile is displayed on a screen, and the viewer can visually confirm whether or not the profile is within the initially calibrated range.