An image reading apparatus includes a reference signal output portion, an image sensor, and an analog front end. The reference signal output portion is capable of outputting a first reference signal and a second reference signal, and changing difference in level between the first reference signal and the second reference signal according to a reference level control signal that is inputted. The image sensor outputs a primary image signal that is an analog signal in which a reference level is a level of the first reference signal that is inputted. The analog front end subjects the primary image signal to offset adjustment according to levels of the second reference signal and an offset control signal that are inputted, and further amplifies a signal having been subjected to the offset adjustment, to output a secondary image signal.