Developing unit having effective developer transportability, and process cartridge and image forming apparatus using the same

A developing unit, comprising:

• a developer carrying member configured to develop a latent image formed on an image carrier with a two-component developer having toner and magnetic carrier by supplying toner to a surface of the image carrier;
• a supplying compartment having a developer supplying transporter configured to supply the two-component developer to the developer carrying member while transporting the two-component developer in an axial direction of the developer carrying member;
• a recovery compartment having a developer recovery transporter configured to transport the two-component developer recovered from the developer carrying member in an axial direction of the developer recovery transporter, the developer recovery transporter transporting the recovered developer in a same direction of the developer supplying transporter;
• and
• an agitation compartment having a developer agitation transporter configured to agitate excess developer not used for a developing process and transported to a downstream side in the supplying compartment and transported to the agitation compartment from the supplying compartment as well as the recovered developer transported to the agitation compartment from the recovery compartment, the developer agitation transporter transporting the agitated excess developer and recovered developer in an axial direction of the developer agitation transporter in an opposite direction of the developer supplying transporter, the agitated excess developer and recovered developer to be transported to the supplying compartment,
• wherein the recovery compartment, the supplying compartment, and the agitation compartment are each separated from one another by one or more separation members and toner is refilled to a developer transport route formed of the recovery compartment, the supplying compartment, and the agitation compartment,
• wherein the developer agitation transporter includes a first screw having a given screw pitch to transport a given amount developer to an upstream end of the supplying compartment from a downstream end of the agitation compartment,
• wherein the developer supplying transporter includes a second screw having a given screw pitch greater than a screw pitch of the first screw.