PURPOSE: To quantitatively measure the gloss irregularity of a coated paper board.

CONSTITUTION: A visible light is emitted from one light source 21 to the outer surface of a coated paper board 23, its reflected light is received by a television camera 24, and a two-dimensional image having obtained bright and dark gradation distribution is Fourier-transformed by an image analyzer 20. Then, the brightness and darkness of the image are bipolarized by using emphasizing coefficient in a specific wavelength range in the case of reversely Fourier- transforming it, the dark image region for forming a closed section is calculated in area as gloss irregular part, and the distribution parameter of the area is output as the measured result.