1. An image forming apparatus comprising: an image bearing member; a developing device which includes a toner bearing member which supplies toner to an electrostatic latent image formed on the image bearing member and develops an toner image; a transfer device which transfers the toner image formed by the toner bearing member onto a recording material; an image density sensor which detects an image density of a reference toner image for controlling the image density developed by the toner bearing member; a toner replenishment device which replenishes the developing device with the toner based on the detection result of the image density sensor; and a controller which makes a control such that a rotation speed of the toner bearing member at the time of forming the reference toner image is higher than the rotation speed of the toner bearing member at the time of forming a normal image.