Tandem type color image forming device

The present invention relates to an image forming device including: toner image forming means for forming a toner image dealing with both colors and a black color to form color or monochromatic (black and white) images, respectively; an intermediate transfer belt onto which the toner image of the respective colors or the black color formed by the toner image forming means is transferred; and transfer means for transferring the toner image on the intermediate transfer belt onto a recording medium, and in particular to a color image forming device which is suitably miniaturized and can realize high image quality, further including a plurality of the toner image forming means per color, and arranging respective toner image forming means by a tandem method, while having the intermediate transfer belt for transferring the toner image. Toner image forming means for forming toner images having chromatic colors of Y, M and C, respectively, are disposed on one side of an intermediate transfer belt, while disposing toner image forming means for forming a black toner image on the other side of the intermediate transfer belt, alone and on a most downstream side of all the toner image forming means. Further, when a toner image on the intermediate transfer belt includes toner having a reverse polarity, a transfer or developing process is controlled to reduce electrostatic attraction force acting on an image carrier, thus providing a color image forming device having a main body reduced in size and capable of faster image formation of a monochromatic image which is more frequently used, and of efficiently forming a color image by suppressing a back-transfer phenomenon and improving color reproducibility.