An A/D converter device includes a zone identifying circuit configured to identify which one of a plurality of level zones a voltage level of an analog output signal is in; a shift voltage generating circuit configured to generate a shift voltage which corresponds to a relevant one of the level zones; an operational amplifier circuit configured to change the analog output signal by means of the shift voltage, the operational amplifier circuit being configured to amplify the changed analog output signal to suit an A/D conversion input range so as to generate an amplified and shifted analog signal; a first A/D converter circuit configured to A/D-convert the amplified and shifted analog signal so as to calculate a first A/D converted value; and a second A/D converted value calculating circuit configured to calculate a second A/D converted value from the first A/D converted value in accordance with the relevant level zone.