Developing device, image forming apparatus

A developing device comprising:

• a developing roller disposed to face, without contact, an outer circumferential surface of an image carrier, and including an aluminum oxide thin film and a resin coat layer, the aluminum oxide thin film being formed on an outer circumferential surface of a base body that is made of a metal including aluminum, the resin coat layer being formed on a surface of the aluminum oxide thin film, the resin coat layer being made of a resin material having electric conductivity;
• a magnetic roller disposed to face, without contact, an outer circumferential surface of the developing roller, and including an aluminum oxide thin film formed on an outer circumferential surface of a base body that is made of a metal including aluminum, the magnetic roller forming a toner layer on a surface of the developing roller via a magnetic brush composed of toner and magnetic carrier, wherein
• an AC impedance Z1 is in a range from 1.0×105Ω to 1.0×106Ω and a surface roughness Ra of the resin coat layer is in a range from 0.057 μm to 0.280 μm, the AC impedance Z1 being obtained when an AC voltage at a predetermined frequency is applied to between the base body of the magnetic roller and the base body of the developing roller in a state where the magnetic brush is formed on the magnetic roller.