A target color signal pair extraction section extracts from color signal pairs each including an input color signal and a counterpart output color signal, a target color signal pair including a target input color signal and a counterpart target output color signal. An output vicinity color signal extraction section extracts from the color signal pairs, output vicinity color signals corresponding to input vicinity color signals, which are located in the vicinity of the target input color signal. A color signal pair accuracy calculation section calculates a color signal pair accuracy of the target color signal pair on the basis of a relation between the target output color signal and the plurality of output vicinity color signals.