A white reference image is inputted to an image sensor with a light source lit up, and white reference data is set every effective photosensor element by inspecting the output signals of the image sensor as to the white reference image (steps S305 and S310). After the input of the white reference image, the light source is extinguished (point e in FIG. 1), a black reference image is inputted to the image sensor (step S315), and black reference data is set every effective photosensor element by inspecting the output signals of the image sensor as to the black reference image (step S320). After the light source is lit up (point f in FIG. 1), the optical image of a subject is inputted to the image sensor, and image data outputted to shading corrections with the white reference data and the black reference data are outputted (step S330)