An A/D converter device is provided, which has a D/A conversion function and changes a resolution of A/D conversion and D/A conversion. The A/D converter device is configured to selectively execute an A/D conversion operation and a D/A conversion operation, by the operation of a control circuit controlling switching of switches according to an ADC/DAC function switching signal supplied from an external side. The A/D conversion operation performs A/D conversion of an input signal voltage inputted via a signal input terminal from an external side and outputs an A/D conversion value of 12 bits. The D/A conversion operation outputs, via a signal output terminal, an analog voltage produced by performing D/A conversion of a digital value supplied from the external side.