In a two-component developing unit, by devising the layout of magnetic poles 6 (particularly a pickup magnetic pole 6b and a trimming magnetic pole 6c) of a magnet member 5 arranged inside a developer carrier 3, an excess portion of a developer G picked up onto the surface of the developer carrier 3 is allowed to drop in the vicinity of the height of the rotational center O of the developer carrier 3, and only the developer G restricted to a predetermined layer thickness is carried and transported to a development region m. A charging member 9 is disposed over a periphery of the developer carrier 3, as required. In addition, the layout of the magnetic poles 6 of the magnet member 5 arranged inside the developer carrier 3 is set variably between the time of development and the time of nondevelopment, and the amount of developer carried on the surface of the developer carrier and transported to the development region m is set to substantially zero at the time of nondevelopment.