An image forming apparatus includes an image bearing member having a surface layer; an electrostatic image forming device for forming an electrostatic image on the surface layer; a developing device, containing at least toner and a carrier, for developing the electrostatic image; a density measuring device for measuring a density of the developed electrostatic image; a layer thickness measuring device for measuring a thickness of the surface layer; and an adjusting device for adjusting toner content in the developing device. The adjusting device adjusts the toner content on the basis of an output of the layer thickness measuring device.