IMAGE FORMING APPARATUS

PROBLEM TO BE SOLVED: To provide an image forming apparatus which forms an image in either a trickle development system or a normal development system, and properly determines a degree of deterioration of a carrier in both systems. SOLUTION: The image forming apparatus 1 has a developing unit 11 that develops a toner image using a developer containing a toner and a carrier, and a concentration control section that supplies a new developer from a detachable supply container 7 so that toner concentration of the developer in the developing unit 11 is maintained constant. The developing unit 11 has a mechanism of discharging a surplus developer so that the amount of developer inside may not exceed a predetermined value. The supply container 7 has a determining section 22 that indicates a content rate of the carrier of the held developer. The image forming apparatus 1 has a life determining section that identifies the determining section of the supply container 7 and estimates the degree of deterioration of the carrier in the developing unit in consideration of the content rate of the carrier of the supply container. COPYRIGHT: (C)2011,JPO&INPIT