An image forming apparatus includes an image carrying member, a developing unit, an image density detector, a toner concentration detector, a toner concentration controller, and an output adjustment unit. The image carrying member forms a reference latent image pattern. The developing unit develops the reference latent image pattern as a reference image pattern with a two-component developer. The image density detector detects an image density of the reference image pattern. The toner concentration detector detects a toner concentration in the two-component developer. The toner concentration controller controls the toner concentration based on the image density detected by the image density detector. The output adjustment unit adjusts a toner concentration sensing level of the toner concentration detector with a sensor control voltage. The toner concentration is controlled by a target voltage with reference to the image density. The toner concentration range is changed by changing the sensor control voltage.