An image forming apparatus includes an image bearing member on which a latent image corresponding to image information is formed, a developing device for developing the latent image on said image bearing member with a developer including carrier and toner, a supplying device for supplying a developer to the developing device, a detector for detecting information corresponding to the magnetic permeability of the developer, and a selecting device for selecting modes on the basis of the information detected by the detecting device, wherein the selecting device can select a first control mode that controls the amount of the developer which is supplied to the developing device by the supplying device on the basis of the information detected by the detector, and a second control mode that controls the amount of the developer which is supplied to the developing device by the supplying device on the basis of the image information.