IMAGE FORMING APPARATUS

PROBLEM TO BE SOLVED: To provide an image forming apparatus estimating toner concentration just before a developing sleeve and performing follow-up control of the toner concentration to a toner concentration target value even when a toner concentration sensor cannot be installed at a position just before the developing sleeve to be originally detected and controlled.SOLUTION: The image forming apparatus includes: a toner concentration sensor 36 for detecting toner concentration in a developing device 31; toner concentration history storage means for storing the detected toner concentration as a history; toner concentration target value setting means for setting the toner concentration target value just before a developing sleeve 32; toner concentration estimation means for estimating the toner concentration just before the developing sleeve 32 using the toner concentration history stored by the toner concentration history storage means; toner supply amount calculation means for calculating toner supply amount to make the toner concentration just before the developing sleeve 32 estimated by the toner concentration estimation means follow the toner concentration target value just before the developing sleeve 32 set by the toner target value setting means; and a toner supply section 33 for supplying the toner supply amount to the inside of the developing device 31.