Patent ID: 7421226

Claim:
A developing device comprising: a predetermined casing structure; a developing sleeve mounted in the casing for supplying toner particles to a latent image area on a peripheral surface of a photoconductive drum while rotating about an axis, the developing sleeve having an immovable sleeve magnet therein, the sleeve magnet including at least a first magnet unit and a second magnet unit, the first magnet unit and the second magnet unit are mounted so that portions of the first and second magnet units located close to the peripheral surface of the developing sleeve have opposite polarities to each other; a pair of magnetic members being disposed in the opposite end portions of the developing sleeve and spaced away from the peripheral surface of the developing sleeve a predetermined distance, each of the magnetic members having an arc shape; and, a magnetic member magnet mounted in the magnetic member, the magnetic member magnet including a third magnet unit facing the first magnet unit and a fourth magnet unit facing the second magnet unit, the third magnet unit and the first magnet unit are mounted to have the same polarity at their opposite facing portion, while the fourth magnet unit and the second magnet unit are mounted to have the same polarity at their opposite facing portions, wherein the first, second, third and fourth magnet units have boundaries disposed so that the boundaries of the first and third magnet units substantially align with one another and so that the boundaries of the second and fourth magnet units substantially align with one another.