PURPOSE: To obtain a copy surface image which is free from a soil on the texture, by forming an image of a reference concentration pattern before copying controlling both the electric charging amount and the exposure volume based on the result of comparison between the concentration signal and the reference signal.

CONSTITUTION: A reference concentration pattern 4 is provided at the right to a scan initiation position 3, and an image is formed before carrying out a copying process. The concentration of this image is detected by an image concentration detector. Thus detection signal is compared with the reference signal at a comparator 16. Based on the result of this comparison, an exposure lamp power supply 18, a charged corona power supply 9 and a development bias power supply 20 are controlled via a control circuit 5. This the control is carried out according to the state of fatigue although the fatigue of a photoreceptor is considerable. Accordingly a copy surface image becomes free from any soil on the texture. In addition, the defects of a surface electrometer can be eliminated since no electrometer is used.