In a color conversion section 10a, a mode judging section 31 judges a mode in effect: a copy mode or a printer mode, according to a mode judging signal. When the copy mode is identified, the mode judging section 31 supplied RGB data to a first color conversion process section 32, and the first color conversion section 32 carries out a first color conversion process in which a transitional color conversion value, which is color-transited from a precise color conversion value and a memory color conversion value, is set as a color conversion value with respect to memory color corresponding data. When the printer mode is identified, the mode judging section 31 supplies the RGB data to a second color conversion process section 33, and the second color conversion process section 33 carries out a second color conversion process in which the memory color conversion value is set as a color conversion value with respect to the memory color corresponding data.