To provide an image forming apparatus which can perform transfer processing while suppressing decrease of image forming speed when forming images sequentially.

When image forming operations are sequentially performed in a monochrome mode for forming monochrome images including black toner images, a control part 41 performs transfer processing during the period (so called inter-paper sheets) since passing of an image forming region through opposing positions of a collecting member 13 and each photosensitive drum 10 by arrival of the next image forming region to the opposing region with a black process unit 9K, and thereby, decrease of collection performance is prevented due to too much accumulation of deposits collected in each collecting member 13. At that time, since a developing roller 14 corresponding to black contacts the photosensitive drum 10, the transfer processing is performed in the monochrome mode without moving the developing roller 14. Therefore, since attachment/detachment operations of each developing roller 14 is not required at performing the transfer processing, the transfer processing can be performed while suppressing decrease of image forming speed in sequential image formation.