Developing unit and image forming apparatus

An image forming apparatus comprising:

• an image carrier;
• a charging unit charging a surface of the image carrier;
• an exposing unit exposing the charged surface of the image carrier to light according to an image data,
• a transferring unit transferring the toner image to paper,
• a developing unit forming a toner image on the surface of the image carrier thus exposed, the developing unit having a plurality of developing rolls over which a developer is conveyed and supplied onto an image carrier which is rotatably supported;
• and
• at least one pair of the developing rolls being adjacent to a developing roll,
• one developing roll of the at least one pair of the developing rolls rotating in a direction opposite to a rotary direction of the image carrier, the other developing roll rotating in the same direction of the rotary direction of the image carrier, the at least one pair of the developing rolls having a regulation member being interposed between the at least one pair of the developing rolls, the regulation member regulating a conveyed amount of the developer, the regulation member being disposed to be opposed to a magnet which is provided within two adjacent developing rolls,
• wherein a polarity of the magnet in the at least one pair of developing rolls is opposed to each other is different from each other.