A color image forming apparatus, which is configured to apply feedback to an image forming condition of an output image based on predicated reflectance of a detection image, comprising: color image forming means (5, 6, 7, 8, 10, 11) for forming images of respective developer colors on a transferring material in accordance with an image forming condition; color measuring means, disposed at a location after fixing means for fixing the images formed on the transferring material, for applying light to images of respective developer colors formed on the transferring material, and detecting reflected light from said images by an optical sensor, characterized by further comprising: predicting means for predicting a predicted reflectance of light reflected from images serving as detection images from the image forming condition of these detection images, setting means for variably setting a detecting condition of said color measuring means in conformity with the predicted reflectance of the detection images such that the output signal of the optical sensor is not buried in noise and is not saturated; and control means for adjusting the image forming condition of images serving as output images, which is a process condition for producing a desired hue of the output images, on the basis of the reflected light detected by said color measuring means in accordance with said detecting condition set by said setting means, wherein said detecting condition is an amount of light of a light source, or said detecting condition is an accumulation time of an accumulation type sensor, or said detecting condition is an accumulation time of an accumulation type sensor and a length of the detected images along a conveyance direction. color image forming means (5, 6, 7, 8, 10, 11) for forming images of respective developer colors on a transferring material in accordance with an image forming condition; color measuring means, disposed at a location after fixing means for fixing the images formed on the transferring material, for applying light to images of respective developer colors formed on the transferring material, and detecting reflected light from said images by an optical sensor, characterized by further comprising: predicting means for predicting a predicted reflectance of light reflected from images serving as detection images from the image forming condition of these detection images, setting means for variably setting a detecting condition of said color measuring means in conformity with the predicted reflectance of the detection images such that the output signal of the optical sensor is not buried in noise and is not saturated; and control means for adjusting the image forming condition of images serving as output images, which is a process condition for producing a desired hue of the output images, on the basis of the reflected light detected by said color measuring means in accordance with said detecting condition set by said setting means, wherein said detecting condition is an amount of light of a light source, or said detecting condition is an accumulation time of an accumulation type sensor, or said detecting condition is an accumulation time of an accumulation type sensor and a length of the detected images along a conveyance direction. predicting means for predicting a predicted reflectance of light reflected from images serving as detection images from the image forming condition of these detection images, setting means for variably setting a detecting condition of said color measuring means in conformity with the predicted reflectance of the detection images such that the output signal of the optical sensor is not buried in noise and is not saturated; and control means for adjusting the image forming condition of images serving as output images, which is a process condition for producing a desired hue of the output images, on the basis of the reflected light detected by said color measuring means in accordance with said detecting condition set by said setting means, wherein said detecting condition is an amount of light of a light source, or said detecting condition is an accumulation time of an accumulation type sensor, or said detecting condition is an accumulation time of an accumulation type sensor and a length of the detected images along a conveyance direction.