1. An image-forming apparatus for forming an image by using a photosensitive member, comprising: means for charging a photosensitive member; means for relatively moving the charging means and the photosensitive member; first applying means for applying to the charging means a first oscillatory voltage such that a Vp/f ratio is about less than 0.08 mm/cycle, wherein the Vp represents a relative moving speed between the charging means and the photosensitive member and the f represents a frequency of the first oscillatory voltage; second applying means for applying a second oscillatory voltage to the charging means such that a Vp/f ratio is about from 0.08 to 0.42 mm/cycle; means for alternatively setting the image-forming apparatus to a normal mode and a halftone mode, the normal mode being for a character image and the halftone mode being for a halftone image; means for connecting the first supplying means to the charging means when the normal mode is set, and connecting the second applying means to the charging means when the halftone mode is set; means for exposing the charged photosensitive member to form an electrostatic latent image; and means for developing the electrostatic latent image.