IMAGE FORMING DEVICE

PURPOSE:To detect an accurate service life and to stabilize image quality according to a degree of developer fatigue by judging the degree of developer fatigue based on a detection value found by a torque detecting means. CONSTITUTION:Torque in the rotation of a stirring roller 16 is measured. Since the fluidity of developer becomes wrong in accordance with the developer fatigue, the load applied on the stirring roller 16 becomes heavy, so that the torque increases. Here, an electrifier output, exposure, a development bias, pretransfer destaticization and a transfer unit output are controlled for a photosensitive drum 1 by utilizing a change of the torque of the stirring roller 16 with a degree of developer fatigue, thereby making image density constant. Additionally, a control part is provided with a microcomputer. It has a judging function which is to judge from the torque value of the stirring roller 16 the degree of developer fatigue and a function which is to judge the end of the service life of the developer when the torque value exceeds a reference level and to stop the execution of an image process.