Patent ID: 7580660

Claim:
A developing roller comprising: a conductive shaft member; a conductive elastic layer formed around the shaft member in a thickness of 0.5 mm to 6.0 mm; and a surface layer, wherein the elastic layer contains carbon black and silicone rubber serving as a binder for the carbon black, the carbon black is in a content of 7% by mass to 17% by mass based on the mass of the elastic layer, the carbon black in the elastic layer has at least two peaks in its particle size number distribution, a minimum diameter peak center in the particle size number distribution is within the range of 10 nm to 40 nm, the elastic layer has density within the range of 1.01 g/cm 3 to 1.07 g/cm 3 , and where a ratio of carbon atoms to silicon atoms (C/Si) in the vicinity of the surface of the elastic layer is represented by X, the ratio of carbon atoms to silicon atoms at a depth of 100 μm from the surface of the elastic layer by Y, and the ratio of carbon atoms to silicon atoms at a depth of 200 μm from the surface of the elastic layer by Z, the X, the Y and the Z satisfy the relationships of the following expressions: 1.50 ≧X/Y≧ 1.10, and 1.10 ≧Y/Z≧ 1.02.