It is known that the mechanism of the charging roller system is the discharge generation in an air gap close to the nip region of the charging roller and the photoconductor. It is important to maintain the stability of discharge for the image quality. Generally, a charging roller has an elastic layer on the surface. The resistance of this elastic layer tends to change with environmental conditions or material property variations.We focus on the fundamental composition that is DC bias charging roller system; the relationship between the resistance of the charging roller and the charged potential of the photoconductor are studied. Consequently, it turns out that the change of electrification potential and generation of uneven electrification are closely related to the resistance of a charging roller. Furthermore, it turns out that uneven electrification is generated due to condition changes which electric discharge is generated at an outlet region of the nip. We found that the above phenomena can be explained by using the relationship between passing time of the air gap close to nip area and the time constant of the roller resistance. From these results, the knowledge for stabilizing image quality is obtained.