Patent ID: 7620352

Claim:
A developing device comprising: a case having a developing opening disposed opposed to a developing area; a cylindrical-shaped developer carry member that is disposed at the developing opening of the case, a part of the developer carry member being exposed, the developer carry member rotating with holding and carrying a developer containing toner and magnetic carriers; a magnet member that is fixed within an internal space of the developer carry member and that has two or more magnetic poles including a developing magnetic pole and a developer peel-off magnetic pole, the magnetic poles being arranged along a rotation direction of the developer carry member; a projection portion formed in a portion of the case that opposes the outer peripheral surface of the developer carry member, the portion of the case also including an area that extends from the developing magnetic pole of the magnet member in the rotation direction of the developer carry member up to the developer peel-off magnetic pole, the magnet member having a normal direction magnetic flux density of 20 mT or less in an area where the projection portion is formed; a clearance formed between an opposed portion of the projection portion and the outer peripheral surface of the developer carry member, the clearance becoming narrowest in the portion of the case; and a magnetic pole disposed firstly on a upstream side of the developer carry member relative to the area of the magnet member having the magnetic flux density of 20 mT or less, the magnetic pole providing a peak value in a peak value area, wherein the projection portion is formed in an area other than the peak value area.