Patent ID: 7925190

Claim:
A developer supply device for supplying a developer comprising a toner and a carrier to a developing unit, the developer supply device comprising: a partially or wholly deformable developer container that holds the developer; and a pump that suctions the developer held in the developer container, together with a gas, and that discharges the developer towards the developing unit, wherein the toner comprises an additive which has a volume average particle size of 50 to 500 nm, the toner has a weight average particle size of 3 to 8 μm, and satisfies a relationship: 1.0 ≦D 4 /D 1≦1.4, where D4 is the weight average particle size of the toner and D1 is the number average particle size of the toner, the carrier has a weight average particle size of 20 to 60 μm, the developer has a carrier concentration of 1 to 30 wt %, and an air layer occupies at least 12% of a capacity of the developer container.