Image forming apparatus having device for detecting concentration of developing agent

An image forming apparatus comprising:

• means for forming a latent image;
• means for developing the latent image with a developing agent, which is detachably mounted in said image forming apparatus and has an identification data unique to said developing means, the developing agent being preset to a predetermined initial toner concentration before said developing means is mounted in said apparatus and the toner concentration being varied from the initial toner concentration in a developing process;
• means for detecting the toner concentration of the developing agent to generate first and second concentration signals which correspond to the initial and varied toner concentrations, respectively;
• means for transferring the identification data and the concentration signal;
• means for storing reference data, and for receiving and comparing the transferred identification data and concentration signals to the reference data, the identification data and the first concentration signal being stored as the reference data in said storing means when the identification data is different from the reference data;
• and
• means for comparing the second concentration signal with the first concentration signal, to supply the toner to said developing mans and maintain the developing agent within a predetermined toner concentration range.