The present invention relates to a developing apparatus used in, for example, an electronic copying machine.
Conventionally known as a developing apparatus of this type is an apparatus which comprises a feeder casing for applying a developing agent to the surface of an image bearing member such as a photosensitive drum, and a developing agent supply unit for supplying the developing agent in a hopper to the feeder casing by rotation. This developing apparatus is provided with various toner detecting switches for detecting the amount of developing agent in the hopper. The switches, which are off while the developing agent exists in the hopper, are turned on when the hopper is emptied of the developing agent. Thus, the presence of the developing agent is detected. However, these conventional switches are low in reliability.