An image reader includes a first image reading unit that reads first image data by scanning one surface of a document at a first resolution corresponding to a magnification ratio and a predetermined first scan cycle; and a second image reading unit that accumulates light radiated from a light source and reads second image data by scanning other surface of the document at a fixed second resolution and a second scan cycle corresponding to the magnification ratio, wherein the second image reading unit controls light accumulation time of the light radiated from the light source to be constant.