Conventionally, in an electrophotographic image forming apparatus, for example, the surface of a photosensitive drum as an image carrier is uniformly and evenly charged by a charging roller as a charging member. The charged surface of the photosensitive drum is exposed to light to form an electrostatic latent image. The formed electrostatic latent image is developed by having a toner adhere as a developer to form a toner image as a developer image. The formed toner image is transferred to a recording medium such as a print sheet and afterwards is fused by applying pressure and heat. The toner remaining on the photosensitive drum without being transferred to the recording medium is removed by a cleaning member.
In recent years, reducing the particle size and lowering the melting point of toners having external additives have been planned, aiming at improving the image quality and speed. As to such toners, because the amount of the external additives increases, cleaning is difficult. Therefore, the external additives adhere onto the charging roller, which generates longitudinal white streaks, and dirt in worse cases due to a charging failure. Then, proposed in Patent Document 1 is a method to remove the external additives by applying to the charging roller a charging voltage of the opposite polarity to that at the image forming time (or in the image forming mode).