An electronic watermark generating apparatus color-converts an RGB image, and divides the color-converted image into a plurality of blocks. Then, the apparatus embeds to-be-embedded information as an electronic watermark into blocks in which an irreversible compression image has been quantized, the image being produced by carrying out quantization on a block-by-block basis, and restores the RGB image by carrying out de-quantization with respect to the blocks. The above apparatus color-converts the restored RGB image, and divides the color-converted image into a plurality of blocks. Thereafter, the apparatus carries out quantization on a block-by-block basis, and extracts to-be-embedded information from the thus quantized blocks. The apparatus embeds the to-be-embedded information as an electronic watermark again in the quantized blocks when it is not checked that the to-be-embedded information has been correctly extracted.