An image forming apparatus, including: a charger, arranged around an image carrier, for charging a surface of the image carrier; an exposure device, arranged around the image carrier, for exposing the surface of the image carrier, after it is charged by the charger, and for forming an electrostatic latent image on the surface of the image carrier; a developer device, having a developer carrier and arranged around the image carrier, for carrying developer with which the electrostatic latent image is developed so as to obtain a developed image; and a transfer device, arranged around the image carrier, for transferring the developed image onto a transfer material. In the image forming apparatus, the developer device has a bias voltage application device for applying developing bias voltage, in which AC voltage and DC voltage are superimposed, between the developer carrier and the image carrier; the AC voltage is intermittently applied; and a waveform in one cycle of each pulse during a term, that AC voltage is applied, does not have a center of symmetry.