Patent ID: 8843033

Claim:
A developer supplier for supplying a developer to a plurality of developing devices including a black developing device, and a color developing device, comprising: a plurality of developer supplying units each configured to supply a developer in which a toner and a carrier are preliminarily dispersed at a given concentration to each of the plurality of developing devices, wherein the plurality of developer supplying units includes a black developer supplying unit configured to supply a black developer in which a black toner and carrier are preliminarily dispersed to the black developing device and a color developer supplying unit configured to supply a color developer in which a color toner other than black toner and carrier are preliminarily dispersed to the color developing device, a proportion of the carrier included in the black developer which is supplied to the black developing device is set so as to be greater than a proportion of the carrier included in the color developer which is supplied to the color developing device, the carrier included in the black developer which is supplied to the black developing device and the carrier included in the color developer which is supplied to the color developing device, consist of the same core material, and a substantially same amount of the developer is contained in the plurality of developing devices, and each developing device includes a developer discharge port to discharge a portion of the developer to an outside of the developing device, wherein a proportion of the carrier in the black developer supplied to the black developing device is substantially 20 wt %; and a proportion of the carrier in the color developer supplied to the color developing device is substantially 10 wt %.