A fluorescent image is obtained by emitting the light with a wavelength which excites a labelling fluorescent substance, a mask is created by a foreign matter area image extracted from an image of foreign matter adhering to the measurement object obtained by emitting light with a wavelength which does not excite the fluorescent substance, and logical multiplication of the mask and the fluorescent image is executed, thereby obtaining a fluorescent image that a foreign matter area is eliminated from the fluorescent image.