An image reading apparatus includes: a frequency modulation unit that generates a clock whose frequency is modulated by an arbitrary modulation cycle; a modulation cycle setting unit that sets the modulation cycle; a driving unit that drives the photoelectric conversion element by the clock; a signal generating unit that generates an analog signal corresponding to a frequency change of the clock; an amplification inversion unit capable of amplifying an alternating current component of the analog signal with an amplification factor corresponding to a setting value set externally, and capable of switching between inversion and non-inversion; a signal superimposing unit that superimposes the analog image signal on an analog signal output from the amplification inversion unit; and a controlling unit that calculates a feature amount, and that controls the amplification factor and the inversion or the non-inversion of the amplification inversion unit based on a calculation result.