DEVELOPING DEVICE

PURPOSE:To prevent a holding plate from making in contact with a developing roller when toner placed on the holding plate is raised to supply it to the developing roller. CONSTITUTION:When toner 20 placed on a holding plate 50 in a housing 30 comes to a condition that it is not detected by a toner sensor 70, air is supplied from an air supplying device 62 to an air bag 60 provided under the holding plate 50 to raise the holding plate 50. The air supplied to the air bag 60 is metered by a cumulative flow meter 63 and, based on the metered results, the height position of the holding plate 50 in the housing 30 is detected. When the holding plate 50 comes at a specified height, air will not be supplied to the air bag 60 and the holding plate 50 will not rise any more even if the toner is not detected by the toner sensor 70.