Abstract: A belt unit (10) includes a drive roller (5), an idle roller (6) and an endless belt (4) stretched around the drive roller (5) and the idle roller (6). The drive roller (5) is supported by a belt frame (8) via bearings (2). The idle roller (6) is supported by the idle roller frame (16) via bearing members (10L, 10R). The idle roller frame (16) is rotatable relative to the belt frame (8) about a rotation axis aligned with the center position of the belt frame (8), with the result that the influence of the deformation of the belt frame (8) is not exerted on the idle roller frame (16).