Image forming apparatus and image formation method

An image forming apparatus comprising:

• a developer;
• a development device that develops an electrostatic latent image into a toner image with the developer;
• and
• an image bearing member that carries the toner image, wherein
• the developer includes an initial developer and a replenishment developer,
• the development device includes:
• an accommodation section that accommodates the developer including at least the initial developer;
• a replenishment section that replenishes the accommodation section with the replenishment developer;
• and
• a developer bearing member that is located opposite to the image bearing member with a space therebetween and that carries and conveys the developer accommodated in the accommodation section,
• the initial developer contains an initial carrier and a toner,
• the replenishment developer contains a replenishment carrier and the toner,
• the initial carrier has a surface with an arithmetic mean roughness Sa1 of at least 0.3 μm and no greater than 1.0 μm,
• a ratio Sa1/Sa2 of the arithmetic mean roughness Sa1 of the surface of the initial carrier to an arithmetic mean roughness Sa2 of a surface of the replenishment carrier is at least 1.2 and no greater than 3.4, and
• a packing volume Vp calculated from equation (1) below is at least 40% and no greater than 70%:
• Vp=100×Y/(Z×DS) (1)
• where in the equation (1),
• Y represents an amount of the developer conveyed by the developer bearing member,
• Z represents an apparent density of the initial developer, and
• DS represents a width of the space between the developer bearing member and the image bearing member.