The present invention provides a digital data comparator having a first selective data inverting circuit inverting a first input data when the sign of the first input data is negative, or outputting the first input data when the sign is positive, a first adding circuit coupled to an output of the first selective data inverting circuit, adding one to the least significant bit when the sign of the first input data is negative, or outputting the first input data when the sign is positive, a second selective data inverting circuit inverting a second input data when the sign of the second input data is positive, or outputting the second input data when the sign is negative, and a second adding circuit adding an output of the first adding circuit and an output of the second selective data inverting circuit.