To prevent influence on color signals requiring no adjustment in adjusting colors out of a color reproduction gamut of an output apparatus, e.g. saturated colors.

Input RGB signals are converted into color signals (JCH) by an input color converting section 201. An intermediate color signal converting section 202 converts the color signals into color signals (J'C'H') having converted intensity, saturation and hue of the color signals while referring to an adjustment table storage means 205, and then, converts the converted signals into J'Ca'Cb' signals. A gamut mapping section 203 converts the J'Ca'Cb' signals into color signals in a color reproduction gamut of the image output apparatus, an output color converting section 204 converts the signals into R'G'B' signals depending on the image output apparatus, and a color decomposing converting section 208 converts the signals into CMYK signals.