A color type converting means 3 generates, from a primary color image, an intensity image in a hue/saturation/intensity space normalized in a cylindrical coordinate system. A region dividing means 6 analyzes the texture of the intensity image and divides the intensity image into a plurality of regions on the basis of the result of the analysis. A density conversion curve generating means 7 generates a density conversion curve for each intensity image by smoothing the histogram for each divided region. A density converting means 8 executes density conversion of the intensity image by using the smoothing a histogram of each region. A region dividing means 5 generates a primary color image by using the intensity image which is density-converted.