To provide an image forming device that prevents reduction in collection performance when a collection member collects deposits.

When images are formed by successive transfer to a transfer object, a transfer process is performed at a predetermined transfer frequency to transfer the deposits such as toner collected by the collecting member 13 temporarily to a photosensitive drum 10 and transfer the deposits from each photosensitive drum 10 to a transfer roller 20. When the images are successively formed in monochrome mode, the frequency of transfer processes is changed according to the type of a medium to be transferred (for example, plain paper, or postcard). In postcard mode, the frequency of transfer process is increased in comparison with that in plain paper mode.