IMAGE FORMING APPARATUS

An image forming apparatus includes a developing device for developing a latent image formed on an image bearing member with a developer comprising non-magnetic toner and magnetic carrier; a toner content detector for detecting information relating to a magnetic permeability of the developer in the developing device; a supplying device for supplying toner into the developing device; and a controller for controlling an operation of the supplying device on the basis of an output of the toner content detector; wherein the controller corrects an amount of a change of the output of the toner content detector per unit content on the basis of an ambient condition information in a main assembly of the apparatus.