Properties of a toner layer, especially toner charge of the toner layer formed onto a developing roller in developing unit influences significantly the developing performance in an electrophotographic developing process. In contact-type non-magnetic single component developing process, the properties of the toner layer change in the developing step due to contact the toner layer with surface of a photoreceptor under the developing electrical field.The toner layer formed onto the developing roller was transferred to a metal plate connected to a bias voltage supply by contact developing method. Controlling the bias voltage applied to the metal plate changed developing electrical field formed on between the developing roller and the metal plate. Charging behavior of the toner layer in this process were studied by measuring the properties of the toner layer before and after the developing step.Amount of toner charge of the toner layer formed onto the developing roller was divided equally by in this developing step. It was clarified that the amount of toner charge changed by charge injection, which depend on the developing electrical field in the contact developing step. In the toner layer consisting of the lower electrical resistivity toner, amount of the toner charge decreased even when the developing electrical field was zero.