In an inkjet printing apparatus using plural line type inkjet printing heads for one color ink, and forming an image by dividing image data into pieces corresponding to the plural printing heads, complementary printing operation using a simple configuration is achieved without causing a substantial decrease in printing speed even when one printing head has a poorly ejecting nozzle. When a one printing head (104) has a poorly ejecting nozzle, a corresponding nozzle of another printing head (an auxiliary printing head, for example) complements printing operation assigned to the poorly ejecting nozzle. At this time, the same piece of divided image data is fed to the one and the other printing heads. Then, the printing operation of the one printing head is made invalid only at the timing of driving the poorly ejecting nozzle, and the printing operation of the second printing head is made valid only at the timing of driving the corresponding nozzle.