One of the major problems of electrophotography in a contact charging roller system is density nonuniformity of a printed image due to anomalous discharges. To find proper countermeasures to such a problem, characterization of the discharge phenomenon is crucial. We developed a measurement technique for micro region discharge currents using a minute electrode embedded in the surface layer of a photoreceptor drum that is capable of quantifying the time variation of the local discharge current. Using a measurement system that utilizes this technique, dependency of the discharge current mode on charging parameters was clarified. Based on changing the charging parameters, discontinuous changes in the discharge modes that affect the nonuniformity of the image density are observed. In this report, in addition to the measurement technique and results, the relationship between the discharge conditions and the density nonuniformity of the image is discussed.