Image forming apparatus having device for detecting concentration of developing agent.

摘要

In an image forming apparatus, a developing unit (18) for developing a latent image on a photosensitive drum is detachably mounted in said apparatus and is provided with a identification signal generator (39A). When the developing unit (18) is replaced with a new one, a identification signal generated from the generator (39A) is compared in a CPU (120) with a reference identification data stored in a memory (122). When the generated identification signal is different from the stored reference identification data, the generated identification signal is stored as a new reference data in the memory (122) and a toner concentration signal generated from sensor (70) is also stored as new reference toner concentration data in the memory (122).