Patent ID: 7460798

Claim:
An image forming apparatus which can change an AC voltage to be applied to a developer carrying member for carrying developer contained in a developing container, said apparatus comprising: a plurality of developer detecting portions configured and positioned to detect a value corresponding to the amount of developer in the developer container; a processing portion configured and positioned to determine the amount of developer in the developer container according to the value when the AC voltage is applied to the developer carrying member; and an image forming portion configured and positioned to form an image with the developer stored in the developing container, wherein said apparatus is configured to change the AC voltage to a first AC voltage and a second AC voltage, and wherein, when the AC voltage is the first AC voltage, said processing portion selects one of said plurality of developer detecting portions and determines the amount of developer in the developer container according to the value detected by said selected developer detecting portion and when the AC voltage is changed to the second AC voltage, said processing portion selects one of said plurality of developer detecting portions and corrects the value detected by selected developer detecting portion and determines the amount of developer in the developer container according to the corrected value.