Patent ID: 8190065

Claim:
A developing device having stirring members for stirring a developer-tank-contained developer containing toner and carrier inside a developer tank while conveying said developer and a developer holder disposed adjacent to said stirring members to supply the stirred developer-tank-contained developer to an electrostatic latent image holder, comprising: a developer replenishing tank for replenishing the toner and the carrier to said developer tank, a toner concentration detecting sensor for detecting the toner concentration inside said developer tank, a discharging mechanism provided in said developer tank to discharge an excessive amount of the developer-tank-contained developer outside said developer tank when the amount of the developer-tank-contained developer inside said developer tank exceeds a predetermined amount, developer amount detecting means for detecting the amount of the developer-tank-contained developer inside said developer tank, and control unit for controlling a replenishment operation of replenishing replenishment toner and carrier from said developer replenishing tank to said developer tank at the time when the toner concentration detected using said toner concentration detecting sensor is lower than a predetermined reference toner concentration, wherein said control unit carries out forced consumption operation for the toner inside said developer tank and replenishment operation for the replenishment toner and carrier in the case that the amount of the developer-tank-contained developer inside said developer tank is judged to be low using said developer amount detecting means.