Toner exhaustion detecting device, developing device, processing unit, and image forming device

The invention discloses a toner exhaustion detecting device used for detecting the exhaustion of a toner of a developing device capable of mounting and disassembling an image forming device. The toner exhaustion detecting device comprises a detection part, an arm, a rotary part and a sensor, wherein the detection part is arranged near a supply part for supplying the toner to a developing agent supporting body of the developing device, and is provided with a surface rotating in the direction of the supply part and changing the rotating range corresponding to the toner amount; the arm is coaxial with a rotating shaft of the detection part, or coaxial with a rotating shaft to which the rotation of the detection part is transmitted, and is exposed out of a developer unit; the rotary part is arranged in the image forming device body, and is contacted with the arm and rotates corresponding to the rotation of the arm when the developing device is arranged on the image forming device; and thesensor detects the rotation of the rotary part.