Developing device and image forming apparatus

A developing device comprising:

• a developer carrying member;
• a first conveyance member conveying a developer in a first direction through a first conveyance path and supplying the developer to the developer carrying member;
• a top wall extending parallel with the first direction;
• and
• a second conveyance member conveying the developer in a second direction through a second conveyance path included in a circulation path along with the first conveyance path, the second conveyance member having a helical second screw around a second shaft, wherein,
• the second conveyance path includes a developer replenishing port, and
• the second conveyance path includes a developer discharge port from which the developer is discharged out of the developing device, the developer discharge port including an opening through the top wall, and
• the second screw has a constant diameter in a second section being a portion extending a predetermined distance in the second direction from an end of the discharge port in the second direction when viewed in a top view, the second screw being configured to convey the developer at a lower speed in the second section than on an upstream side of the second section,
• wherein the second conveyance path and the second screw are configured such that, during operation of the developing device, developer is backed up in the second conveyance path upstream of the second section such that the backed up developer is forced into the developer discharge port.