IMAGE FORMING APPARATUS

PROBLEM TO BE SOLVED: To provide an image forming apparatus which is free of an abnormal increase in toner concentration (TC) and causes none of problems of ground staining, toner scatter, etc., by accurately detecting TC of a developing unit. SOLUTION: The image forming apparatus has an image carrier which carries a toner image, a two-component developing device which holds a developer for forming the toner image on the image carrier, a toner concentration sensor which detects the toner concentration in the developing device based upon permeability of a developer, a toner supply control means of performing toner supply control according to the output of the toner concentration sensor, and a temperature/humidity detecting means of detecting temperature and humidity. The toner supply control means varies upper- and lower-limit values of a target toner concentration value according to the temperature and humidity detected by the temperature/humidity detecting means. COPYRIGHT: (C)2007,JPO&INPIT