Patent ID: 8588656

Claim:
A developing device comprising: a developer tank that stores a developer; a partition that partitions an internal space of the developer tank into a first conveyance path along a longitudinal direction of the partition, a second conveyance path opposing to the first conveyance path with the partition interposed therebetween, and first and second communicating paths communicating with the first conveyance path and the second conveyance path at both ends in the longitudinal direction of the partition; a first developer conveying member that is provided in the first conveyance path, and has a first rotation shaft which rotates around an axial line thereof, and a first conveying blade provided around the first rotation shaft, the first developer conveying member conveying the developer stored in the developer tank in a first developer conveying direction along the axial line of the first rotation shaft with rotation motion of the first conveying blade following rotation of the first rotation shaft; a second developer conveying member that is provided in the second conveyance path, and has a second rotation shaft which rotates around an axial line thereof, and a second conveying blade provided around the second rotation shaft, the second developer conveying member conveying the developer stored in the developer tank in a second developer conveying direction, which is opposite to the first developer conveying direction, along the axial line of the second rotation shaft with rotation motion of the second conveying blade following rotation of the second rotation shaft; a double spiral blade that is provided facing the first communicating path on a downstream side from the first conveying blade of the first developer conveying member in the first developer conveying direction, and comprises an inner spiral blade that is provided around the first rotation shaft of the first developer conveying member and conveys the developer stored in the developer tank in a first direction among axial line directions of the first rotation shaft with rotation motion following rotation of the first rotation shaft, and an outer spiral blade that is provided around the inner spiral blade and conveys the developer stored in the developer tank in a second direction among the axial line directions; and a developing roller that bears and conveys the developer, wherein the first developer conveying member is configured so that the first developer conveying direction is a same direction as the first direction, and wherein the inner spiral blade is a cone-shaped general spiral blade whose internal diameter is constant and external diameter becomes continuously smaller as advancing in the first direction, and the outer spiral blade is an annular general spiral blade whose external diameter is constant and internal diameter becomes continuously larger as advancing in the second direction.