To upgrade reproducibility in the case of printing by using a special ink by gradation converting a pixel vale of a specific color in a main printer, thereby obtaining the gradation converted pixel value.

An input unit 1 inputs engraving plate data formed by another engraving system to an arithmetic unit 2 through a LAN (local area network). The unit 2 separates the data into color separating process to generate separate color engraving data, and conducts color matching calculations and gradation conversion. The conversion is obtained as gradation conversion functions of respective process colors corresponding to the specific color pixel values of γc(v), γm(v), γy(v) and γk(v), pixel values of the respective colors corresponding to the specific reference pixel values of Cs, Ms, Ys, Ks, and gradation converted pixel values of the respective colors corresponding to the gradation conversion values of the respective colors corresponding to the specific pixel values of C, M, Y and K.