To reproduce a primary color as truly as possible in converting color reproducing area between machines with different color reproducing areas and to achieve excellent color reproduction without losing gradation.

An RGB signal inputted from a color display 1 is converted into uniform color space data of a CIELAB surface color system by a color space converting means 2. The color reproducing area of the CIELAB surface color system data is compressed or expanded by using a converting function stored in a color reproducing area storage means 3a by a color reproducing area converting means 3. The converted uniform color space data is converted into a CMY (K) signal of a color printer 5 and outputted by a color space reconverting means 4. The color reproducing area converting means 3 is instructed to select one converting function among plural converting functions stored in the color reproducing area storage means 3a by a selecting instruction means 6.