The charging mechanism of toner in the mono-component non-magnetic toner developing system was studied experimentally. A microscopic current measurement technique was used to analyze the dynamics of toner charging. A current was observed to flow through each part (i.e. the development roller, doctor blade, and supply roller) during rotation of the roller with toner attached on its surface. The current holds a strong relationship to the toner charge and supplied toner mass. Development rollers with various surface properties were prepared for this study. The currents and toner charge were measured for each roller both before and after a running test. The experimental results confirmed that the toner charge decreases during the running tests. Finally design features of a high durability development roller will be proposed.