An image forming apparatus includes a developer, a development device, and an image bearing member. The developer includes an initial developer containing an initial carrier and a replenishment developer containing a replenishment carrier. The initial carrier has a surface roughness Sa1 of at least 0.3 ?m and no greater than 1.0 ?m. A ratio Sa1/Sa2 of the surface roughness Sa1 of the initial carrier to a surface roughness Sa2 of the replenishment carrier is at least 1.2 and no greater than 3.4. The packing volume Vp calculated from equation (1)Vp=100?Y/(Z?DS) was at least 40% and no greater than 70%. In equation (1), Y represents an amount of the developer conveyed by a developer bearing member. Z represents an apparent density of the initial developer. DS represents a width of a space between the developer bearing member and the image bearing member.

An image forming apparatus includes a developer, a development device, and an image bearing member. The developer includes an initial developer containing an initial carrier and a replenishment developer containing a replenishment carrier. The initial carrier has a surface roughness Sa1 of at least 0.3 ?m and no greater than 1.0 ?m. A ratio Sa1/Sa2 of the surface roughness Sa1 of the initial carrier to a surface roughness Sa2 of the replenishment carrier is at least 1.2 and no greater than 3.4. The packing volume Vp calculated from equation (1)Vp=100?Y/(Z?DS) was at least 40% and no greater than 70%. In equation (1), Y represents an amount of the developer conveyed by a developer bearing member. Z represents an apparent density of the initial developer. DS represents a width of a space between the developer bearing member and the image bearing member.

A developing device includes a developing roller and a developing magnetic pole. The developing roller is disposed to face an image carrier across a predetermined gap. The developing magnetic pole is provided in the developing roller so as to be displaced between first and second magnetic pole positions. When the developing magnetic pole is at the first magnetic pole position, a magnetic field is generated at a first position in the gap. When the developing magnetic pole is at the second magnetic pole position, a magnetic field is generated at a second position in the gap. When a circumferential speed ratio of the developing roller to the image carrier is increased, the developing magnetic pole is displaced toward the second magnetic pole position, and when the circumferential speed ratio is decreased, the developing magnetic pole is displaced toward the first magnetic pole position.

A developing device includes a developing roller and a developing magnetic pole. The developing roller is disposed to face an image carrier across a predetermined gap. The developing magnetic pole is provided in the developing roller so as to be displaced between first and second magnetic pole positions. When the developing magnetic pole is at the first magnetic pole position, a magnetic field is generated at a first position in the gap. When the developing magnetic pole is at the second magnetic pole position, a magnetic field is generated at a second position in the gap. When a circumferential speed ratio of the developing roller to the image carrier is increased, the developing magnetic pole is displaced toward the second magnetic pole position, and when the circumferential speed ratio is decreased, the developing magnetic pole is displaced toward the first magnetic pole position.

A unit for an image forming apparatus includes a developing unit that includes a developing roll and a voltage applying section, and a cleaning unit that includes a cleaning blade which contacts with the image holding member and cleans a surface of the image holding member, wherein the developing roll is provided with an interval of 100 m to 300 m with respect to the image holding member, and holds an electrostatic charge image developer including a carrier and a toner whose a volume average particle diameter is 2 m to 5 m on a surface of the developing roll, and the voltage applying section applies an alternating voltage in which an alternating-current component is applied on a direct current component to the developing roll, the following expression being satisfied: 34Toner Volume Average Particle Diameter [m]Alternating-Current Component Frequency [kHz]60.

Magnetic one-component toner has toner particles including: a toner base particle containing at least a binder resin and a magnetic powder; and an external additive attached to the surface of the toner base particle. The toner base particle contains a nigrosine dye. The external additive contains strontium titanate particles of which the surface is hydrophobically treated. The amount of nitrogen element in toner particles is 0.5 mass % or more but 5 mass % or less. The Abs value representing the amount of nigrosine dye that dissolves when toner particles are immersed in methanol as expressed in terms of light absorbance is 0.2 or more but 2.0 or less. The volume resistivity of strontium titanate particles is 1.0 E+7 [.Math.cm] or more but 1.0 E+10 [.Math.cm] or less.