The inventive image processing apparatus takes steps of 1) dividing an image to be processed into numerals of blocks; 2) determining whether a block is a color block or not; 3) determining whether the image is a color image or not based on the rate of color blocks to the entire blocks. Thereby, valid color pixel rate can be obtained at blocks belonging to a color region even though an image is almost monochrome but partially colored. Accordingly, the inventive image processing apparatus can appropriately determine whether the image is a color image or not.