When, in a two-color image forming apparatus, a first visible image is formed on a photosensitive drum, and sequentially a second visible image is formed on the drum on which the first visible image remains, said second visible image being different in color from said second visible image, a cylindrical non-magnetic sleeve rotates in a direction opposite to a rotation of a permanent magnet equipped with the sleeve, thereby enabling a developer to be conveyed in a direction opposite to a rotation of the permanent magnet.