An image forming apparatus having plural developing devices, comprising: a photosensitive member arranged rotatably in one direction and holding an electrostatic latent image corresponding to an original image; a developing sleeve rotatably arranged in each developing device at a position confronting said photosensitive member to transport a developer; a device for simultaneously driving for rotation of each of said developing sleeves in said developing devices; and an adjusting mechanism for adjusting operation of said developing devices so that in a region where said developing sleeves confront with said photosensitive member, a developer packaged density (F) in said developing device arranged at an upstream side in a rotational direction of said member is larger than that of said developing device arranged at a downstream side in the rotational direction of said member, which isF=Vd/Ds,where Vd is an amount of the developer passing between said developing sleeve and said photosensitive member per hour, and Ds is a distance between said developing sleeve of said developing device and said photosensitive member. Then, a high quality image may be reproduced by the apparatus, which has improved reproducibility RSI of density of a reproduced solid obtained by the upstream device and improved reproducibility RLI of density of a reproduced line image obtained by the downstream device.