A multi-value code image generation part generates a multi-value code image by assigning first code information, which is obtained by encoding a dot pattern in a specific area, to each growth core. A multi-value code image affine transformation part performs affine transformation on the multi-value code image. A multi-value code image assignment part assigns second code information to each of the growth cores before the affine transformation according to the first code information of at least one growth core after the affine transformation, which growth core neighbors close to the growth core before the affine transformation. A dot pattern development part develops the dot pattern for the specific area at each of the growth cores before the affine transformation according to the second code information.