An image reading apparatus according to an embodiment includes an image reading unit configured to generate reference data by reading a reference surface and to generate image data by reading a sheet. A reference unit has a reference surface. A shading correction unit determines whether a portion of the reference surface includes a contaminant based on image data generated by the image reading unit reading the portion of the reference unit. When the portion of the reference surface is determined to not include a contaminant, the shading correction unit generates reference data based on the image data generated by the image reading unit reading the portion of the reference surface determined to not include a contaminant.