There is described an image forming apparatus, which prevents an occurrence of worm-shaped image irregularities even in the high-speed developing operation to form a high quality image. In the image forming apparatus, the contact developing employing a two components developer including toner and carrier is conducted in such a manner that the latent image bearing member and the developer bearing member move in directions being opposite relative to each other at a developing region where the latent image bearing member and the developer bearing member are opposed to each other. The frequency of the AC current component and a line velocity of the latent image bearing member fulfill a condition indicated as follow: vp/f.ltoreq.70condition 1 where vp (mm/sec) is the line velocity of the latent image bearing member and f (kHz) is the frequency of the AC current component.