In an image forming apparatus, a photoconductor and a charge roller are in contact with each other and configured to rotate together at linear velocity v (millimeters/second). In this structure, a DC voltage is applied to the photoconductor and the charge roller while they are not rotating. In this state, parameters such as voltage, linear velocity, pressure contact force between the photoconductor and the charge roller are selected so that the ratio w/v (seconds), where w is the interval between two discharge marks occurring on surface of photoconductor, is between 0.005 to 0.035.