An electrophotographic copying apparatus comprises a photoconductive drum, a charger for electrically charging the drum, an exposure unit for exposing the drum to form a latent image on the drum which correspond to the pattern of a document, a developer unit for developing the latent image, using one-component toner, a transfer unit for transferring a toner image to a paper sheet and a fixer unit for fixing the toner image.In copying the document pattern, a document density-copy density characteristic, i.e. .gamma. characteristic, is set in accordance with the document density. According to the .gamma. characteristic the amount of exposure and the bias voltage to be applied on the developer unit are varied.