There is provided a differential comparator circuit that is mounted on a test apparatus for testing a device under test outputting differential signals including noninverted signals and inverted signals. The differential comparator circuit includes: a difference signal subtracting circuit operable to compute and output a difference signal indicative of a difference between the noninverted signal and the inverted signal; a first threshold value subtracting circuit operable to compute and output a first threshold voltage indicative of a difference between a first comparative voltage generated based on ground potential of the device under test and a reference voltage generated based on the ground potential of the device under test; and a first comparing circuit operable to compare the difference signal and the first threshold voltage to output a comparison result.