The measurement unit measures a
voltage by converting it from analog to digital and outputs a measurement value. The
changeover unit, being connected to a battery and a reference
voltage source generating a highly accurate fixed
voltage, selects one of them and applies it to the measurement unit. The voltage value output unit makes the
changeover unit select a fixed voltage generated by a predetermined
voltage source, makes the measurement unit measure it as a reference voltage and generates calculation-use information for calculating a voltage value from a measurement result based on a measurement value of the fixed voltage and a voltage value of the reference voltage. The voltage value output unit, when making the
changeover unit select a voltage of the battery and making the measurement unit measure it, uses the measurement value of it and the calculation-use information to calculate and output a voltage value of the battery.