There is provided an image stabilizing apparatus which is capable of keeping a toner concentration and a printing density constant when, toner consumption is small, and further which is systematically simple. The image stabilizing apparatus comprises a control portion for controlling a toner replenishment amount in a toner replenishing apparatus depending on a toner concentration detected by a toner concentration sensor and a print coverage of a document detected by a print coverage detecting portion, and controlling, when the print coverage of the document detected by the print coverage detecting portion is less than a predetermined value and such documents continue, so as to discharge a predetermined amount of toner to the image bearing member by developing forcibly, and then replenish the same amount of toner as the predetermined amount by the toner replenishing apparatus.