Abstract: Disclosed is an apparatus for detecting a resistance value of a resistor sensor through three signal lines with high detection accuracy. In the apparatus, a reference resistance element is inserted in a current path of a reference current, first and second voltages across the ground and first and second signal lines are respectively held in first and second holding portions and a third voltage across the terminals of a reference resistance element is held in a third holding portion. The first and second voltages held in the first and second holding portions are output simultaneously and the third voltage held in the third holding portion is output at a timing different from the timing when the first and second voltages are output. A differential amplifier detects the third voltage and a differential voltage.