Patent ID: 8086143

Claim:
An image forming apparatus comprising: an image bearing member configured to bear an electrostatic latent image thereon; a developing device, which is configured to develop the electrostatic latent image with a developer including a toner and a carrier to form a toner image on the image bearing member and which includes: a developer bearing member configured to bear the developer to develop the electrostatic latent image with the developer at a development region; a developer containing portion configured to contain the developer; a developer supplying passage including a developer feeding member configured to feed the developer in a first direction parallel to an axial direction of the developer bearing member to supply the developer to the developer bearing member; and a developer agitating passage including a developer agitating member configured to feed a mixture of the developer, which is fed to a downmost stream side of the developer supplying passage without being used for developing the electrostatic latent image, and the developer, which passes through the development region and is directly returned to the developer agitating passage, in a second direction opposite to the first direction to an upstream side of the developer supplying passage while agitating the mixed developer, wherein the developer agitating passage is separated with a partition from the developer supplying passage except for at least both end portions thereof in the first and second directions; a developer supplement supplying device configured to supply a developer supplement including the toner and the carrier to the developing device to mix the developer supplement with the mixed developer; and a developer discharging device configured to discharge an excess of the developer from the developing device to replace at least a part of the carrier in the developer with the carrier in the developer supplement, wherein the carrier includes a particulate core material and a cover layer located on the surface of the particulate core material, and wherein the cover layer includes a binder resin and a first particulate material, wherein the cover layer satisfies the following relationship: 1<( D 1 /h )<10, wherein D 1 represents a volume average particle diameter of the first particulate material in units of micrometer, and h represents an average thickness of a resinous portion of the cover layer in units of micrometer.