A belt unit includes a drive roller, a follower roller and an endless belt looped around the drive roller and follower roller, and formed of a resilient material. The drive roller transfers a first force based on the driving force to the endless belt to circularly move at a first velocity at a first boundary between the drive roller and the endless conveying belt. The first velocity provides a first fluctuation. The endless belt transfers a second force based on the first force to the follower roller to rotate. The endless belt moves at a second velocity at a second boundary between the follower roller and the endless belt. The second velocity provides a second fluctuation. A transmission parameter with respect to at least one of the drive roller, the follower roller and the endless belt is set so that the second fluctuation is smaller than the first fluctuation.