To provide an image forming apparatus that suppresses deterioration in a primary transfer belt and an image carrier, and image transfer failure when a sheet is cardboard in a monochrome image formation mode.

An image forming apparatus 10 includes: a primary transfer drive roller 32; a secondary transfer belt 41; a secondary transfer roller 42; and a backup roller 46. The backup roller 46 lays over the secondary transfer belt 41 on the upstream side of the secondary transfer roller 42 in a sheet conveyance direction 91, and displaces in a direction to contact and separate with/from the primary transfer drive roller 32. When a sheet is cardboard in a monochrome image formation mode, the backup roller 46 is disposed to a position closer to the primary transfer drive roller 32 than a position in a full-color image formation mode.