Patent ID: 8406641

Claim:
An image forming apparatus comprising: a developing device; a toner supply device that is detachably mounted to the image forming apparatus and supplies toner to the developing device; a toner supply controller that controls the toner supply from the toner supply device to the developing device based on predetermined conditions; a toner empty determiner that determines that no toner is left in the toner supply device when the amount of toner supplied from the toner supply device to the developing device is lower than a threshold, characterized in that the developing device comprises: a developer container for storing a developer including the toner and a magnetic carrier; a toner supply port that leads the toner supplied from the toner supply device into the developer container; and, a toner supply sensor arranged near the toner supply port to detect the amount of toner supply, the toner supply device includes a storage for recording the amount of toner supply detected by the toner supply sensor every time a toner supply operation is made, and, the toner supply controller corrects the amount of toner supplied from the toner supply device to the developing device, based on the moving average of multiple toner supplies recorded in the storage.