An image forming apparatus capable of executing a continuous image forming operation for forming images on a plurality of recording materials, said apparatus comprising: an image forming portion including an image bearing member capable of carrying an electrostatic image, and a developing device configured to develop an electrostatic image formed on said image bearing member into a toner image, using a developer including toner and carrier; an exchangeable developer container configured to supply the developer into said developing device; a content sensor configured to detect information relating to a toner content in said developing device; an exchange detecting portion configured to detect of an exchanging operation of said developer container; and a controller configured to control supply of the developer from said developer container into said developing device so that a detection result of said content sensor is a target toner content characterized in that said controller is configured to control said image forming portion so that, when the toner content in said developing device based on the detection result of said content sensor continuously meets, during the continuous image forming operation, a condition that it is lower than a first threshold which is lower than the target toner content, the continuous image forming operation is interrupted, and when exchange of said developer container is detected by said exchange detecting portion in a state that the continuous image forming operation is interrupted, the continuous image forming operation is resumed irrespective of the toner content in said developing device, and the image is formed on at least one recording material. an image forming portion including an image bearing member capable of carrying an electrostatic image, and a developing device configured to develop an electrostatic image formed on said image bearing member into a toner image, using a developer including toner and carrier; an exchangeable developer container configured to supply the developer into said developing device; a content sensor configured to detect information relating to a toner content in said developing device; an exchange detecting portion configured to detect of an exchanging operation of said developer container; and a controller configured to control supply of the developer from said developer container into said developing device so that a detection result of said content sensor is a target toner content characterized in that said controller is configured to control said image forming portion so that, when the toner content in said developing device based on the detection result of said content sensor continuously meets, during the continuous image forming operation, a condition that it is lower than a first threshold which is lower than the target toner content, the continuous image forming operation is interrupted, and when exchange of said developer container is detected by said exchange detecting portion in a state that the continuous image forming operation is interrupted, the continuous image forming operation is resumed irrespective of the toner content in said developing device, and the image is formed on at least one recording material.