The development of a compact, high image quality, and maintenance-free electrophotographic color printer suitable for personal computers, EWS, and so on has been demanded. Another important demand is for the development of an electrophotographic printer for which less replacement and less disposal of material is necessary. With this in mind, the authors have been developing a contact type mono-component nonmagnetic development system utilizing a soft and conductive development roller, and a simultaneous development and cleaning process in order to realize a still simpler printing process. In this process, the residual toner remaining on the photoreceptor at the transfer process is cleaned simultaneously by the same development unit, while the latent image is developed by the same unit. Miniaturization of the printer system has been realized and the disposal of the waste toner has become unnecessary, since there is no cleaning unit. The authors have also developed a color toner suitable for a contact type mono-component nonmagnetic development system and have applied it to a four- drum-tandem type color printer. This paper describes the principle of the simultaneous development and cleaning process and the development characteristics of the four-drum- tandem color printer utilizing the development system.