Patent ID: 7181147

Claim:
An image forming apparatus comprising: a developing unit having a developer container configured to contain developer comprising toner and carrier, a stirring member configured to stir the developer, a developer holding member configured and positioned transport the developer from inside of the developer container to an image holding member, and a storage medium configured to store various parameters; a toner supply member configured to supply the toner to the developer container; and a controller configured to determine a replacement timing of the developing unit, wherein said storage medium stores a first parameter related to the amount of usage of the carrier corresponding to the amount of the toner supplied by said toner supply member and a second parameter related to the amount of usage of the carrier corresponding to the amount of operation of said developing unit, and wherein said controller determines the replacement timing of said developing unit based on the first and second parameters stored in said storage medium, wherein the amount of operation of said developing unit corresponds to the amount of operation of the developer holding member or the stirring member.