PURPOSE: To form an image obtained by visualizing color identifying information included in an image signal by coding an image signal obtained from an image pickup device in the inserted state of a color sorting filter into an optical part to the three primary colors based upon the permeability of the filter.

CONSTITUTION: White light generated by a light source box 1 is converted into illuminating light having prescribed spectrum by a light source color forming device 2. The illuminating light outputted from the device 2 is guided up to an object O through a light guide 3. Reflected light reflected from the object O illuminated by the illuminating light and having a monochromatic image pickup element provided with sensitivity characteristics broad in the whole visual light area or a wavelength area more than the visual light area is detected by a TV camera 4 and converted into an image signal for the image of the object O. An image processing part 5 applies processing such as the visualization of color identifying information to the output image signal from the camera 4 to code the image signal to the three primary colors based upon the permeability o the color sorting filter.