PURPOSE: To eliminate A/D converting error by stablizing a slice value and to generate and output an arbitrary analog signal when any abnormality is generated.

CONSTITUTION: A reference voltage outputted from reference power sources 10 and 11 is compared with the analog signal of a measuring object by respective comparators 12 and 13 of a measured signal normality/abnormality judgement part 2 and when the analog signal is out of a slice range decided by the reference voltage, such a state is detected. Based on the detected result, the A/D converting operation of the analog signal is controlled and when the analog signal is out of the slice range, malfunction such as A/D converting error is prevented.