An image forming device in a continuous mode forms monochrome images on a plurality of recording media in succession. A transfer member is disposed in confrontation with a plurality of photosensitive members. In the continuous mode, a control unit controls a reverse-transfer unit to perform a reverse-transfer operation on at least one of a plurality of collecting members such that the excrescences are transferred from the at least one of the photosensitive members onto the transfer member in a medium interval. A switching unit sets a contact state to a first contact state during the reverse-transfer operation in the continuous mode such that one of the developing rollers for black contacts one of the photosensitive members for black and that remaining ones of the developing rollers are separated from remaining ones of the photosensitive members.