Image forming apparatus having a high gamma photoreceptor

The invention provides an apparatus for forming an image in which there is provided a photoreceptor includes an imaging surface for forming an electrostatic latent image thereon in response to an exposure light. The photoreceptor has a light decay characteristic so that the potential of the imaging surface is not decayed in an initial period of exposure and the potential of the imaging surface is sharply decayed in a middle period of exposure. A laser beam generator is used for scanning and exposing the imaging surface with a laser beam to write thelatent image on the imaging surface. A generator drive circuit includes a signal generator for generating a reference wave signal and is adapted to receive an image density signal, to modulate the image density signal on the basis of the reference wave signal and to drive the laser beam generator in accordance with the modulated image density signal.