A shading correction apparatus includes: a light irradiating unit configured to scan an original document; a reference plate located in a scanning area of the light irradiating unit; a detecting unit configured to receive reflected light from the original document or the reference plate of light irradiated by the light irradiating unit; a first control unit configured to classify plural areas of the reference plate, which are divided in a direction perpendicular to a traveling direction of the light irradiating unit, as plural blocks, scan the reference plate for each of the blocks with the light irradiating unit, and detect valid areas of the plural blocks; and a second control unit configured to set the valid areas of the plural blocks as adopted areas used for shading correction.