PURPOSE: To provide a method for controlling toner concentration by which toner concentration is normally kept at the time of restarting the recording of a copying machine.

CONSTITUTION: In an image recorder in which an electrostatic latent image formed on a photosensitive drum 8 is developed with two-component developer 23 and then recorded on a recording paper, magnetic field is generated so as to influence the developer 23, and the toner concentration is controlled by using a toner concentration sensor 28 which detects the change of the magnetic permeability of the developer 23. When recording for the set number of papers is finished, the time until restarting the next recording is measured, and every time the measured time attains specified time, control voltage controlling the intensity of the generated magnetic field of toe sensor is corrected by specified voltage Vc for the specified time (tr).