Patent ID: 7769327

Claim:
A developing device comprising: a developing roller, including: a rotating sleeve which rotates while holding two-component developer composed of toner and magnetic carrier on an outer surface having a plurality of grooves that extend in a direction parallel to an axis of the rotation, wherein a pitch between adjacent grooves on the outer surface of the rotating sleeve ranges from 1.25 mm to 4 mm, wherein a width of each groove ranges from 0.2 mm to 0.35 mm, and wherein a depth of each of the grooves ranges from 0.08 mm to 5.00 mm, and a magnetic member, provided inside the rotating sleeve in such a manner as to be unrotatable, for attracting the two-component developer onto the outer surface of the rotating sleeve; and a blade, provided outside the rotating sleeve with a gap from the outer surface of the rotating sleeve, for scraping off a part of the two-component developer, the magnetic member including a magnet for controlling a magnetic flux density in the gap to range from 85 mT to 150 mT.