An image reading apparatus includes: light-receiving elements arranged in a main-scanning direction to perform photoelectric conversion pixel by pixel; AD converter units that convert each piece of analog data photoelectric-converted by the light-receiving elements into parallel pieces of digital data; a storage unit that stores therein each of the digital data converted by the AD converter units; a converter unit that reads the digital data stored in the storage unit and converts the read digital data into serial data in the main-scanning direction; a readout control unit that changeably controls a readout start pixel and a readout end pixel of the serial data in the main-scanning direction; and a period change unit that changes a period in which the converter unit converts digital data into serial data in the main-scanning direction based on the readout start pixel and the readout end pixel.