Patent ID: 7904009

Claim:
A development device which, in image forming processing using a two-component developer, converts a latent electrostatic image borne upon a latent electrostatic image bearing member into a visible image, comprising: a developer bearing member which rotates while bearing a two-component developer, and which conveys said two-component developer to a development region which opposes said latent electrostatic image bearing member; a magnet which is fixedly disposed in the interior of said developer bearing member, and which has a plurality of magnetic poles; and a developer regulation member which opposes said developer bearing member at a position on the upstream side of said development region with respect to the direction of rotation of said developer bearing member, while providing a gap between them; wherein said developer regulation member comprises at least a magnetic member, the thickness of said magnetic member along said rotational direction of said developer bearing member is between 0.2 mm and 0.4 mm inclusive, wherein the cross sectional area of said magnetic member, as calculated by multiplying the thickness of said magnetic member along said direction of rotation, and the height of said magnetic member along the radial direction of said developer bearing member, is between 1.0 mm 2 and 2.1 mm 2 inclusive, and wherein the magnetic permeability of said magnetic member is between 300 and 495 inclusive; and wherein: if the distance over said developer bearing member, from the position thereupon which the center of said magnetic member along said rotational direction opposes, to the position thereupon at which the magnetism of that magnetic pole which is disposed closest to said position is a maximum, is termed L (mm), and the diameter of said developer bearing member is termed D (mm), then said magnetic member is disposed within the range in which the relationship 0≦L/D≦0.044 holds.