An image reading apparatus includes: a reading unit which reads an original as an object to be read in a main scanning direction every time a command signal is inputted; a command unit which inputs the command signal to the reading unit; a conveying unit which conveys at least one of the original and the reading unit so as to change a relative position between the reading unit and the original in a sub scanning direction; a signal output unit which outputs a displacement signal every time the relative position is changed by a predetermined amount; and a control unit which controls the command unit. The command unit which operates in a first mode to output the command signal to the reading unit at a predetermined time interval and in a second mode to output the command signal to the reading unit at a timing synchronized with the displacement signal.