in a flash a / d converter including a plurality of differential amplifier circuits and a plurality of voltage comparator circuits , a regulator circuit is provided . the regulator circuit automatically regulates a bias voltage of each of the plurality of differential amplifier circuits in a differential amplifier circuit array to make an output dynamic range for the differential amplifier circuits match an input dynamic range for the plurality of voltage comparator circuits . therefore , even if the input dynamic range for the voltage comparator circuits is narrowed with reduction in a power supply voltage , the output dynamic range for the differential amplifier circuits and the input dynamic range for the voltage comparator circuits match , thus resulting in a high a / d conversion accuracy .