PURPOSE: To detect the deterioration of the developer at the same time, and prevent drop of image concentration so as to keep the picture quality favorably, by applying an electric field to the developer, and detecting the toner concentration, and optically detecting the difference from the concentration at the time of not applying electric field.
CONSTITUTION: While electric field is not applied to the developer, a photo electrode detector 4c detects an apparent toner concentration f1. When an electric field is applied by electrodes 4a, 4b, the toner particles positively charged are attracted to the side of cathode 4b and migrate. The concentration f2 detected in this state is the concentration of noncharged toner. By detecting the difference of these concentrations f1, f2, a solenoid control circuit 8 is operated, and the toner is supplied from a toner bottle 5. In this constitution, since the rate of active toner contributing to the development is detected by compensating for the deterioration of the developer, the picture image concentration may be constantly maintained for a long period of time, so that the picture quality may be maintained favorably.
HIRATA TOSHITAKA
KAWAKUBO TOSHIO
KATOU TOSHIBUMI
