Image forming apparatus with replenishment developer device

An image forming apparatus, comprising:

• an image bearing member on which an electrostatic image is formed;
• a developing apparatus having a developing container containing a developer including toner and carrier, a developer carrying member provided at the developer container for carrying and conveying the developer to develop the electrostatic image;
• a supply device which performs a supply operation for supplying a replenishment developer including toner and carrier to the developing container;
• and
• a developer discharging port provided at the developing container for discharging the developer out of the developing container;
• wherein the supply device comprises replenishment developer detecting means for detecting information regarding a ratio of the toner in the replenishment developer in the supply device, and
• wherein the supply device changes an operation condition in the supply operation in accordance with a detection result of the replenishment developer detecting means.