An optical writing system with at least two laser diodes capable of correcting hue deviations. The optical writing system is capable of correcting dot forming positions in the main scanning direction, and setting values for correction through an external key operation unit stored in a phase shift amount register by way of a CPU included in a main controller, and by applying values for arbitrarily shifting picture element clock phases for respective laser diodes. Thus, frequency fluctuations and characteristic changes in the laser diodes over time are compensated, positional precision with respect to a synchronization point is assured for respective laser diodes, picture images at the terminating edge in the main scanning direction is stabilized, and subtle hue variations can be reduced in half tone image portions during repeated full color image formations.