An image forming apparatus of the present invention includes an exposure portion to form an electrostatic latent image by exposing the surface of an image carrier, a developing device to form a developer image by developing the electrostatic latent image formed on the image carrier with a developer and a detecting device that has a specified detecting area on the image carrier and detects the quality change of an image formed on the detecting area. The image forming apparatus of the present invention further includes a means to decide a minimum examination image forming area that is nearly in accord with the detecting area of the detecting device by forming an examination image for the image change detection on the image carrier by the exposure portion and the developing device, detecting the formed examination image by the detecting means and changing the examination image forming area according to the detection result of the detecting device.