outputting the input signal without performing the subtraction process a switch 8 whose one switch terminal is connected to a signal input terminal whose other switch terminal is connected to an output side of sample hold circuits 5 6 and whose common terminal is connected to an input side of the arithmetic processor a comparator 3 for comparing an output from the signal amplifier with the reference voltage to binarize the output and a switch 11 for connecting an output side of the signal amplifier to an input side of the sample hold circuits wherein the arithmetic processor carries out a changeover between the operation of performing the subtraction process of the reference voltage from the input signal to output the result and the operation of outputting the input signal without performing the subtraction process based on an output from the comparator thereby decreasing the circuit scale and substantially eliminating occurrence of an error application_number US 10525898 A description the embodiments of the present invention will be described in detail by reference to the drawings fig2 is a schematic circuit diagram t o show the first embodiment of the present invention in fig2 an analog signal to undergo the a d conversion.