In accordance with an embodiment, an image reading apparatus comprises a sensor configured to read an image in a main scanning direction; a first reference plate; a second reference plate; and a processor configured to determine a parameter for shifting shading correction data on the basis of first reference data obtained through reading on the first reference plate by the sensor and second reference data obtained through reading on the second reference plate by the sensor, set the shading correction data on the basis of data obtained through the reading on the first reference plate by the sensor, acquire image data at each reading position in the sub-scanning direction by the sensor and carry out shading correction on the image data on the basis of the shading correction data shifted according to a shift amount at the each reading position obtained from the parameter.