Belt unit and image-forming device having the same

An image-forming device comprising:

• a drive roller that rotates upon receiving a driving force from a drive motor;
• a follower roller rotatable as a result of rotation of the drive roller;
• and
• an endless belt that is looped around the drive roller and follower roller, and formed of a resilient material;
• wherein 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 providing a first fluctuation,
• wherein the endless belt transfers a second force based on the first force to the follower roller to rotate, the endless belt moving at a second velocity at a second boundary between the follower roller and the endless belt, the second velocity providing a second fluctuation,
• wherein 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.