The A/D converter device includes a comparing section and an abnormality judging section. The comparing section compares a voltage of its signal transfer line connected between its input multiplexer and its A/D converting section through its sample-hold section with a predetermined abnormality judging voltage. The abnormality judging section is configured to apply a reference voltage to the signal transfer line in synchronization with an A/D conversion cycle thereof on condition that its A/D converting operation thereof is not interrupted, and to determine presence of abnormality in the A/D converter device if an comparison result of the comparing section does not match an expected value corresponding to the reference voltage.