A new method is proposed for correcting the ac component of the color registration error in the paper feeding direction in a tandem-type color laser printer. The main factor of the ac color registration error is the fluctuation of the angular velocity of organic photoconductive drums caused by gears with runout in multiple gear systems. In order to express the fluctuation mathematically, the kinematical relation between a pair of gears with runout is constructed and it is extended into a multiple gear system. Also, the specific reduction ratio in the multiple gear system is proposed as a necessary condition for the correction of the ac color registration error. With the ac color registration error obtained by integrating the angular velocity, the optimization problem is formulated in terms of the installation phase of the gears with runout. A continuous evolutionary algorithm is used to find the optimal installation phases.