PURPOSE: To improve the operability of the correction of shading distortion and to miniaturize a device by preliminarily supplementing the sensitivity irregular data of a line sensor and the light quantity distribution irregularity data of a lens and performing a multiplication for fetched image information based on this supplement, for the white level correction of a scanner.

CONSTITUTION: When the reflected light from an object via a lens 28 is made incident to a run sensor 20, the outputted information is inputted in a subtracter 30 because the noise of the image output is reduced by a clamper 22 and a sample and hold F23 via an amplifier 21. After a black level correction is performed for the inputted information to a subtracter 30 based on the correction information from the black correction data ROM 32 changed into an analog signal via a D/A converter 33, a white level correction is performed for the information based on the correction information converted into the analog signal by each of D/A converters 35 and 37 from each of white correction memories 34 and 36 by multipliers 31a and 31b.