An ink-jet color printing apparatus is comprised of a rotary drum that bears the paper or other medium to receive the color printing and rotates in a primary scanning direction. A group of yellow ink-jet heads, a group of magenta ink-jet heads, a group of cyan ink-jet heads and a group of black ink-jet heads are provided, with each group of ink-jet heads arranged in the secondary scanning direction parallel to the axis of rotation of the drum. These ink-jet heads form simultaneously dot lines of four different colors. Groups of ink-jet heads of respective color are comprised of a plurality of ink-jet heads arranged in the primary scanning direction so as to form a plurality of dot lines constituting a single scanning line. A single picture element is formed by a dot matrix having n.times.m possible positions on a plurality of dot lines. Intermediate colors and color densities thereof can be achieved by combinations of several kinds of colored inks and dot patterns formed on a single matrix.