Developing unit and image forming apparatus

An image forming apparatus comprising:

• an image retainer of which a latent image is formed on a surface;
• a transfer unit that transfers the visible image on the surface of the image retainer to a surface of a medium;
• a fixing unit that fixes the visible image on the surface of the medium;
• a first developing unit that is disposed in opposition to the image retainer and that develops the latent image on the surface of the image retainer into a visible image;
• and
• a second developing unit that is disposed adjacently to the first developing unit,
• wherein the first and the second developing units each includes:
• a developer retainer includes a magnet member and a retaining member, the magnet member having magnetic poles, the retaining member being provided on an outer circumference of the magnet member and retaining a developer having magnetism to be sucked on a surface of the retaining member by a magnetic force of the magnet member;
• a developing vessel receives the developer internally, and which includes a retainer receiving portion, a first agitation portion and a second agitation portion, the retainer receiving portion receiving the developer retainer, the first agitation portion being adjacent to the retainer receiving portion, the second agitation portion being adjacent to the first agitation portion;
• a first conveyance member is received in the first agitation portion and that conveys the developer in the first agitation portion in a first conveyance direction;
• and
• a second conveyance member is received in the second agitation portion and that conveys the developer in the second agitation portion in a second conveyance direction which is reverse to the first conveyance direction,
• wherein the first developing unit includes a magnetic member, and
• the magnetic member is disposed between the developer retainer of the first developing unit and the second conveyance member of the second developing unit.