This paper introduces a new method to reduce periodic density unevenness caused by eccentric rotation of the photoconductor drum and development roller in an electrophotographic printer. In a previous study, a method for controlling periodic density unevenness by using developing bias was proposed. The developing bias is controlled periodically to correct density unevenness. However, no control effects are obtained in low density images; rather, the control somewhat increases the density unevenness.In this study, we developed a new method that reduces the periodic density unevenness through modulation of both charging bias and developing bias based on the rotational periods of the photoconductor drum and development roller. Each bias is periodically changed such that the changes in the developing field due to the eccentric rotation of the photoconductor drum and development roller are cancelled, thus suppressing the periodic density unevenness. Experiments we conducted confirmed that the new method improves periodic density uniformity better than the previous method. The new method guarantees density uniformity is obtained without the use of high-precision components.