To provide an image reading apparatus capable of performing correction so as to uniformize gray balance even when a change in the gray balance in a main scanning direction is caused in an LED light source or the like.

The line reference white board data of one line is created from reference white board read data, the line original data of one line is created from original read data, and the gray balance correction data of one line is created from the line reference white board data and the line original data and stored in a memory. A shading correction means for performing shading correction is provided, a reference original is set and read, and the gray balance correction data is stored in a storage means. When reading normal images, a reference white board is read, shading data is created, then an original is read, the original read data is shading-corrected on the basis of the shading data and the gray balance correction data to achieve original image data, and thus the shading correction for correcting gray balance variation in the main scanning direction as well is performed.