Patent ID: 7577388

Claim:
A developing roller comprising: (I) a developing sleeve that is made of nonmagnetic material, and that holds and conveys a developer containing a toner and a magnetic carrier; and (II) a magnetic member that is fixed inside the developing sleeve, wherein the magnetic member comprises: (i) a development magnetic pole that corresponds to a development area where the developer is applied; (ii) a before-development magnetic pole that is provided at an upstream side of the developer-conveying direction with respect to the development magnetic pole, and that has a polarity different from the development magnetic pole; and (iii) an after-development magnetic pole that is provided at a downstream side of the developer-conveying direction with respect to the development magnetic pole, and that has a polarity different from the development magnetic pole, wherein θ 1 , θ 2 and θ 3 satisfy the following formulas: θ 1 >90°; and θ 1 +θ 2 >θ 3 , wherein θ 1 represents an open angle between peak positions of magnetic flux density in normal-direction to the outer peripheral surface of the developing sleeve of the development magnetic pole and the before-development magnetic pole, θ 2 represents an open angle between peak positions of magnetic flux density in normal-direction to the outer peripheral surface of the developing sleeve of the before-development magnetic pole and the after-development magnetic pole, and θ 3 represents an open angle of peak positions of magnetic flux density in normal-direction to the outer peripheral surface of the developing sleeve of the development magnetic pole and the after-development magnetic pole.