Patent ID: 8099001

Claim:
A developer cartridge that is attachable to and detachable from a developing housing, the developing housing supporting a developer carrier and comprising a drive gear for transmitting a driving force to the developer cartridge, the developer cartridge comprising: a cartridge housing that is configured to accommodate developer; a first passage portion that is provided in the cartridge housing to allow a passage of a detection light for detecting an amount of the developer accommodated in the cartridge housing; an agitator that is provided in the cartridge housing and is configured to agitate the developer by the driving force; a transmission gear that is configured to mesh with the drive gear to transmit the driving force to the agitator, the transmission gear meshing with the drive gear when the developer cartridge is installed in the developing housing; and a second passage portion configured to allow the passage of the detection light and that is provided in a center part of the transmission gear through which a rotational axis of the transmission gear extends.