An image forming apparatus incorporating: an image forming body; and a developing unit having a developer carrier, a magnetic field generator, a developer restriction member, a first conveyer, and a second conveyer, wherein the magnetic field generator has: a main magnetic pole; pickup magnetic pole; and a strip-off magnetic pole, wherein the developing unit satisfies following conditions: (a) the second conveyer is a screw conveyer having an outer diameter within 24 mm-30 mm, rotating speed of 300-500 rpm, (b) the pickup magnetic pole is arranged at an angle of 25.degree.-60.degree. downstream with a line connecting a rotation centers of the developer carrier and the second conveyer, (c) the strip-off magnetic pole is arranged at 60.degree.-80.degree. upward with the line,(d) a transporting capability of the first conveyer is larger than that of the second conveyer.