Developing device with toner containing a toner particle and a zinc stearate particle, and process cartridge, image forming apparatus, and image forming method

A developing device comprising:

• a developer container that accommodates an electrostatic image developer including toner containing a toner particle and a zinc stearate particle externally added to the toner particle, a ratio (DT/DS) of a volume-average particle size (DT) of the toner particle to a volume-average particle size (DS) of the zinc stearate particle being 1.9 or more, and the volume-average particle size (DS) of all zinc stearate particles in the toner are within the range of 1.0 μm to 6.0 μm, inclusive;
• a developer carrier that has a surface on which the electrostatic image developer is carried and that supplies the toner to an image carrier;
• a supply conveyor that supplies the electrostatic image developer to the surface of the developer carrier while conveying the electrostatic image developer in an axial direction of the developer carrier;
• a mixing conveyor disposed on a lower side of the supply conveyor in a gravity direction, the mixing conveyor conveying the electrostatic image developer in the axial direction of the developer carrier while mixing the electrostatic image developer, the mixing conveyor conveying the electrostatic image developer in a direction opposite to a direction in which the supply conveyor conveys the electrostatic image developer;
• and
• a partition disposed between the supply conveyor and the mixing conveyor,
• wherein the electrostatic image developer is moved from the supply conveyor to the mixing conveyor through a first passage provided at one end portion of the partition, and
• the electrostatic image developer is moved from the mixing conveyor to the supply conveyor through a second passage provided at the other end portion of the partition.