Patent ID: 8521069

Claim:
A developing device to be installed in an electrophotographic image forming apparatus including a photoconductor drum that is to have an electrostatic latent image formed on a surface thereof, the developing device comprising: a developer vessel that accommodates a developer containing a toner and a carrier; a toner supply port for supplying the toner into the developer vessel; a developing roller that is disposed in the developer vessel and that rotates while carrying the developer to supply the toner onto the surface of the photoconductor drum having the electrostatic latent image formed thereon; a developer conveying passage that is disposed between a position in the developer vessel where the toner is supplied and the developing roller; and a developer conveying helical member that is rotatably disposed in the developer conveying passage to convey the developer in the developer conveying passage to the developing roller, wherein the developer conveying passage includes: a first developer conveying passage associated with the toner supply port and a second developer conveying passage associated with the developing roller, the first developer conveying passage and the second developer conveying passage being defined by a partitioning plate extending in parallel to an axial direction of the developing roller; and a pair of communicating paths that establish a communication between the first developer conveying passage and the second developer conveying passage at opposite sides in the axial direction, and the developer conveying helical member includes a first developer conveying helical member disposed in the first developer conveying passage and a second developer conveying helical member disposed in the second developer conveying passage, wherein the first and second developer conveying helical members include a rotary shaft and a helical blade fixed to an outer peripheral surface of the rotary shaft, and at least one of the first and second developer conveying helical members includes an end blade at one end of the rotary shaft at a downstream side in a conveying direction of the developer, wherein the end blade includes a circumferential-direction agitating blade portion whose radial projecting size gradually increases toward the downstream side in the conveying direction; and a helical blade portion integrally wound around an outer periphery of the circumferential-direction agitating blade portion in the same helical direction as that of the helical blade, wherein, in the first and second developer conveying passages, the first and second developer conveying helical members convey the developer in directions opposite to each other, and the end blade agitates the developer in a circumferential direction of the rotary shaft at the downstream side in the conveying direction, such that the developer circulates through the first and second developer conveying passages.