Patent ID: 8737886

Claim:
An image forming apparatus, the apparatus comprising: a photosensitive drum to transfer a toner supplied according to an electrostatic latent image onto a printing medium, and to form an image on the printing medium; a developing roller to supply the toner to the photosensitive drum; and a developing unit to supply, to the developing roller, a two-component developing agent, in which the toner and a carrier are mixed, wherein the developing unit comprises: a transferring unit to transfer the two-component developing agent in an axial direction of the developing roller; and a preparatory agitation unit disposed on an end part of the transferring unit and comprising an agitation screw that has a large diameter, and to mix the newly-supplied toner and the carrier, and when a process speed at which the photosensitive drum forms an image on the printing medium is approximately 300 mm/s, a width of the printing medium at which the photosensitive drum forms an image is equal to or less than approximately 216 mm, and if an amount at which the agitation screw protrudes from a surface of the two-component developing agent in an upward direction is r (mm), a pitch of the agitation screw is P (mm), a number of revolutions of the agitation screw is R (rps), and time for mixture and agitation is T (s), then the preparatory agitation unit satisfies the following inequality: r > 20 ⁢ P RT .