PURPOSE: To make it possible to determine the quantity of the degree of the nonuniformity of metal painting in a shape close to the image of human observation with the eyes by performing a light emitting step and a light receiving step continuously at a specified interval at a plurality of places.

CONSTITUTION: When an optical probe 1 is moved at a specified speed or lower, the laser beam emitted from a light projector 2 is reflected from a surface to be measured 6. The output of the light signal from a photodetector 4 is fetched to a controller 7 every time when a preset measuring interval has elapsed with the position signal, which is sent out of a rotary encoder 5. In this way, the probe 1 is continuously moved by a specified distance on the surface to be measured. Thus, the degree of the continuous change of the amount of the reflected light with respect to the moved distance can be fetched to the controller as the signal data. When the analysis starting signal is sent from the keyboard of a personal computer 10, the signal is fetched to the personal computer 10 from the controller 7 through a cable 8. After waveform analysis, statistic processing and graphic processing, the results are displayed on a monitor 9.