The invention provides an image reading apparatus that scans an image from an original document including: a light source that irradiates a light to the original document; a photoelectric conversion element; a driving mechanism that relatively moves either one of the photoelectric conversion element or the original document in a predetermined direction with respect to the other; a detection sensor that detects a vector amount of movement of either one of the photoelectric conversion element or the original document in the predetermined direction with respect to the other so as to output a detection signal for each vector amount of movement that corresponds to a minimum unit of a reading area of the image; and a control unit that executes one cycle of operations each time when the detection signal is outputted from the detection sensor.