An image reading apparatus includes an image capturing module, a reference member, a light source for emitting light to the reference member, a foreign object determining module for determining whether or not a foreign object appears in a specific image, and a position determining module for determining whether the foreign object exists on the image capturing module side or on the reference member side, based on an absolute value of a difference between a gradation value in a region included in two images and corresponding to a region where the foreign object appears when the foreign object appears in the specific image. One image is an image of the reference member captured under illumination of light with a first light quantity from the light source, and other image is an image of the reference member captured under illumination of light with a second light quantity from the light source.