In a developing device of the present invention, in a developing zone where an image carrier and a developer carrier face each other, the developer carrier carrying a developer thereon moves at a linear velocity of 150 mm/sec or above, but below 500 mm/sec. The amount of the developer conveyed to the developing zone by the developer carrier is between 65 mg/cm 2 and 95 mg/cm 2 . A magnetic flux generated on the developer carrier in the developing zone by a magnetic pole has a flux density having an attenuation ratio of 40 % in the direction normal to the developer carrier. The flux density in the direction normal to the developer carrier, as measured on the surface, is between 100 mT and 200 mT. Magnetic grains, which constitute the developer together with toner grains, have a saturation magnetization value of 40 x 10 -7 x 4π Wb·m/kg or above, but below 50 x 10 -7 x 4π Wb·m/kg.