1. A multi-pass image forming apparatus comprising: a photosensitive medium; an exposure unit for forming a plurality of electrostatic latent images on the photosensitive medium; a plurality of developers containing color toners of yellow, cyan, magenta and black, respectively and sequentially disposed to face the photosensitive medium for developing the plurality of electrostatic latent images using two toners having different polarities and colors in one development process and for forming a multi-color image in at least two development processes; and an intermediate transferring unit for having toner images transferred thereon from the photosensitive medium that overlap to form the multi-color image; wherein the exposure unit includes a plurality of sub-driving units for selectively being turned on/off to charge the photosensitive medium to potentials corresponding to an image region onto which toners having different polarities and colors are transferred and a non-image region on which the image is not formed; wherein the plurality of the sub-driving units includes a first sub-driving unit and a second sub-driving unit, wherein the first sub-driving unit is turned on to charge the photosensitive medium with a latent image potential V 1 by which the toner having a negative polarity can be transferred, and the second sub-driving unit is turned on to charge the photosensitive medium with a non-latent image potential V md by which the image is not formed, and both the first sub-driving unit and the second sub-driving unit are turned off to maintain the photosensitive medium with a surface potential V 0 by which the toner having a positive polarity can be transferred.