An A/D conversion device includes an input-data storage unit storing therein a plurality of digital values obtained after A/D conversion so that each of the digital values is positioned at a fixed address according to a delay amount, a coefficient-data storage unit, a coefficient-data computation unit that, when a digital-filter process performing request is inputted, calculates an order and a filter coefficient based on a filter characteristic set beforehand, arranges calculated filter coefficients in order of delay amount, respectively, and stores the filter coefficients in the coefficient-data storage unit so that each filter coefficient is positioned at a fixed address according to the corresponding delay amount, and a digital-filter computation unit respectively reading a digital value from the input-data storage unit and a filter coefficient from the coefficient-data storage unit for each delay amount and performing a filter computation based on the read values for each delay amount.