A color space transformation matrix calculating method is provided that calculates a color space transformation matrix which transforms colors in a first color space to colors in a second color space. The method optimizes a plurality of constant color-space transformation matrices, so that each of the constant color-space transformation matrices is adjusted to transform each standard color in the first color space to each goal color in the second color space, which correspond to each of the standard colors. The method further calculates interpolation functions for each matrix element of a color-space transformation matrix applied for the entire gamut of the first color space, based on the constant color-space transformation matrices.