We propounded a four-photoconductor tandem system to meet the demand for colorization and high-speed performance of copiers and printers [1]. Since then, we have developed optical units for the system, to cope with some problems typically found in color machines, such as the flexibility of the optical configuration and the reduction of displacements among four color dots. The optical design that we are to introduce here has some essential features to deal with some of the difficulties referred to above.To facilitate the optical configuration, we employ singlet scanning lenses for each color in the optical unit. And we apportion refractive powers between two surfaces of the scanning lens effectively, to reduce wave front turbulence. Next, to reduce displacements among four color dots in sub-scanning direction, we set the bow of each color scanning line to the same side, by locating a pair of two-piled scanning lenses symmetrically to the deflecting device and flipping one of the pair vertically. In addition, we corrected displacements among four color dots by employing the rotating structures for light source units.