Patent ID: 8340554

Claim:
A developing device comprising: a developer receptacle for storing a developer containing a toner and a magnetic carrier; first and second developer conveying passages formed by sectioning the interior of the developer receptacle by a partitioning wall so as to communicate with each other at both the ends of the partitioning wall; first and second conveying members provided inside the first and second conveying passages, respectively, for agitating and circulatively conveying the developer in the first conveying passage and the developer inside the second conveying passage, in the opposite directions to each other; a developing roller which supports the developer in the second developer conveying passage and supplies the toner contained in the developer to a photoreceptor drum; a toner supply port disposed in the first conveying passage to receive added toner; and an agitator disposed in the first conveying passage under the toner supply port, characterized in that the first conveying member includes: a rotary shaft; and, a helical blade provided on the outer periphery of the rotary shaft, the agitator is formed coaxially with the first conveying member so as to be rotatable independently from the first conveying member, and the agitator includes a circular helix formed around the outer periphery of the helical blade of the first conveying member, and wherein the circular helix has the same pitch as that of the helical blade of the first conveying member and the helical blade is arranged on the inner side of the inside diameter of the circular helix.