Image forming device

An image forming device includes an optical system for forming an electrostatic latent image on a photosensitive body by exposure of an original in light, a development system for developing the electrostatic latent image, and a control system for controlling the optical system and the development system. The control system detects the concentration of a toner in a developing agent tank, calculating a difference between the detected toner concentration and a predetermined toner concentration, replenishing the toner to the developing agent tank until the detected toner concentration makes a recovery to the predetermined toner concentration, clocking a time period for the recovery and controlling at least one of the amount of the exposure light and the amount of the toner adhering to a photosensitive body based on the clocked time period for the recovery.