PURPOSE: To correct the nonlinearity of an analog input signal without increasing the logic scale of the hardware by giving an analog signal to one input of plural comparators and imparting reference voltages which are ranged at an unequal interval to the other inputs.

CONSTITUTION: An analog input signal AIN imparted to an analog input terminal A1 and divided voltages Vr1-Vr7 resulting from dividing reference voltages VR1-VR6 imparted respectively from standard voltage input terminals V1-V6 are compared respectively by comparators C1-C7 in a comparator group 4. Then divided voltages imparted to the voltage division inputs of the comparators C1-C7 are set to an equal and proper interval by changing intermediate reference voltages VR2-VR5 properly. Thus, it is possible to correct an analog input signal having nonlinearity without increasing the logic scale of the hardware.