Abstract: An image forming apparatus has full- and half-speeds as image forming speeds. In the full-speed mode, a detected voltage value conforming to the electrostatic capacity between a developing roller and plate antenna of a process cartridge is converted to the amount of toner remaining in the apparatus. In the half-speed mode, on the other hand, the amount of remaining toner is found using a value obtained by adding a correction value ? to the detected voltage value conforming to the electrostatic capacity between the developing roller and the plate antenna. As a result, the amount of toner can be sensed accurately even if the electrification conditions of an image carrier change.

Abstract: An image forming apparatus has full- and half-speeds as image forming speeds. In the full-speed mode, a detected voltage value conforming to the electrostatic capacity between a developing roller and plate antenna of a process cartridge is converted to the amount of toner remaining in the apparatus. In the half-speed mode, on the other hand, the amount of remaining toner is found using a value obtained by adding a correction value &dgr; to the detected voltage value conforming to the electrostatic capacity between the developing roller and plate antenna. As a result, the amount of toner can be sensed accurately even if the electrification conditions of an image carrier change.