An electrophotographic image-forming apparatus and a charging voltage control method therefor. The electrophotographic image-forming apparatus has a charging roller applying a predetermined voltage to a photosensitive medium, a developing roller for developing with a developing agent an electrostatic latent image formed on the photosensitive medium by a laser scanning unit, a transfer roller transferring onto a sheet of recording paper the image developed by the developing agent, and a high voltage power supply (HVPS) applying predefined voltages to the respective rollers. The apparatus also includes a charging roller resistance detection unit detecting a resistance value of the charging roller, a transfer roller resistance detection unit detecting a resistance value of the transfer roller, and a control unit determining the charging voltage to be applied to the charging roller based on the charging roller resistance value detected by the charging roller resistance detection unit and the transfer roller resistance value detected by the transfer roller resistance detection unit. Accordingly, the present invention can adaptively select a charging voltage to be applied to the charging roller depending upon the changes of the transfer roller resistance value and the charging roller resistance value.