Developing device and image formation apparatus

A developing device comprising:

• a first transport passage;
• a first transport member disposed in the first transport passage and configured to rotate and thereby transport developer along the first transport passage in a first transport direction, the developer containing toner;
• a second transport passage;
• a second transport member disposed in the second transport passage and configured to rotate and thereby transport the developer along the second transport passage in a second transport direction;
• and
• a developer carrier disposed along the first transport passage and configured to carry the developer supplied from the first transport passage, wherein
• the second transport passage is composed of an upstream section and a downstream section with respect to the second transport direction,
• the second transport passage communicates with the first transport passage via a first communication passage and a second communication passage, the first communication passage being connected to the upstream section, the second communication passage being connected to the downstream section, and the first transport passage, the first communication passage, the second transport passage, and the second communication passage constituting a circulation passage for circulating the developer,
• the upstream section is configured to receive refill toner, and
• V1<V2<V3, where V1 denotes an average transport speed of the first transport member, V2 denotes an average transport speed of a section of the second transport member within the upstream section of the second transport passage, and V3 denotes an average transport speed of a section of the second transport member within the downstream section of the second transport passage.