A color image forming apparatus for automatically setting an image forming condition includes an electrophotographic photosensitive member movable along an endless path; an electrostatic latent image forming device for forming electrostatic latent images for different colors on the photosensitive member; a plurality of developing device containing different color toners, operable corresponding to the electrostatic latent image; a transfer device for overlaying developed images sequentially onto a transfer material; a monitor image forming device for forming a monitor image; a control device for controlling the image forming condition on the basis of the monitor image; wherein detection of the monitor images for the respective developing device is completed with one-half the time required for the photosensitive member to rotate for image formation by all of the developing device.