An image-reading apparatus includes a light dividing unit that divides irradiated light so that a part of the light having a first wavelength is diffracted, and a part of the light having a second wavelength is transmitted; a first light measuring unit that measures an intensity of light entering into a first measuring area, and outputs first measurement information indicating the measured intensity; a second light measuring unit that measures an intensity of light entering into a second measuring area, and outputs second measurement information indicating the measured intensity; an image-forming unit that forms an image of a subject for reading in the first measurement area, and that forms a virtual image in the second measurement area using light diffracted by the light dividing unit; and a generation unit that corrects the first measurement information on the basis of the second measurement information.