| 摘要 |
PROBLEM TO BE SOLVED: To prevent two-component developer from being influenced by magnetic field from an electrifier even when the magnetic brush electrifier of an adjacent image forming part on an upstream side is arranged proximately to a developing device, and to accurately detect the toner concentration of the developer by a permeability detection system. SOLUTION: Respective image forming stations disposed along a transfer belt 130 possess the developing device on the upstream side and the magnetic brush electrifier on the downstream side of a photoreceptor drum 3 with respect to the drum 3, so that the electrifiers 2 of the 1st to the 3rd stations on the upstream side are positioned at the back of the developing containers 31 of the developing devices 1 in the 2nd to the 4th stations. A sensor 43 detecting the toner concentration by detecting the permeability of the developer in a stirring chamber R is installed at the side wall part of the container 31 on the stirring chamber R2 side. In order to prevent the influence of the magnetic field from a supporting sleeve 54 including the magnet 55 of the electrifier 2 on the upstream side from being exerted on the developer in the chamber R, a sealing member 56 made of a magnetic member is provided between the developing device 1 and the electrifier 2. |
