A transfer unit includes: an intermediate transfer belt that (i) holds a toner image that has been transferred, at a primary transfer part, from a photoreceptor drum and (ii) rotates to move a surface holding the toner image; and a secondary transfer belt that comes into contact, at a secondary transfer part, with the intermediate transfer belt. The transfer unit (i) transfers the toner image from the intermediate transfer belt to a sheet conveyed to the secondary transfer part and (ii) includes an intermediate transfer belt cleaning unit that removes and collects toner from the toner image holding surface of the intermediate transfer belt. The transfer unit also includes secondary transfer power source for sequentially applying, to the secondary transfer belt, (i) a first voltage for generating an electric field that transfers normally-charged toner from the secondary transfer belt to the intermediate transfer belt and (ii) a second voltage for generating an electric field that transfers oppositely-charged toner from the secondary transfer belt to the intermediate transfer belt. Therefore, the toner from the secondary transfer belt can be suitably transferred to an intermediate transfer belt, and the secondary transfer belt can be desirably cleaned.