DEVELOPING DEVICE

PURPOSE:To stop development automatically at the time of a decrease in toner concentration by selecting the saturation magnetism and particle size of magnetic carriers and the napping height of a developer, and inhibiting a developer with less than specific concentration from being carried onto a developing roll. CONSTITUTION:A magnetic sleeve 2, magnet roll 3, agitating roll 4, and control plate 5 are provided in a developer hopper 11, and the developer 6 consisting of toner and carriers is supplied onto a nonmagnetic sleeve 2, controlled by the control plate 5 to layer thickness (g), and carried to a photosensitive body 1. The values of the particle size and saturation magnetism of magnetic carrier affect the ability to convey the developer, so the saturation magnetism of carrier particles and a gap (g) are selected to inhibit the developer from being conveyed in case of a decrease in toner concentration. Thus, trouble such as carrier tailing is prevented in case of the decrease in concentration.