A color copying machine includes a plurality of image forming sections having rotatable photoconductive drums, respectively. One of the drums, which is used for forming images in black, is rotated by a first drum drive motor, and the other drums are rotated by a second drum drive motor. A plurality of transfer devices are arranged to oppose the image carriers, respectively. A paper sheet is sequentially moved to positions opposing the drums and clamped between the drums and transfer rollers so as to transfer images on the drum to the paper sheet. When a image formation is performed by using the image forming section for black, the first drive motor is operated and the second motor is stopped. The transfer rollers opposing the drums for other than black are moved to positions wherein these transfer rollers are away from the corresponding drums.