A developing unit includes 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 each other. In the pair of the developing rolls, one
developing roll rotates in a direction opposite to a rotary direction of
the image carrier, and the other developing roll rotates in the same
direction of the rotary direction of the image carrier. A regulation
member is interposed between the pair of the developing rolls. The
regulation member regulates a conveyed amount of the developer. The
regulation member is disposed to be opposed to a magnet which is provided
within the two adjacent developing rolls. A polarity of the magnet in the
pair of developing rolls opposed to each other is different from each
other.