A belt unit includes: a pair of roller members spaced from and opposing each other in a first direction, each of the roller members having an axis extending in a second direction; an endless belt extending around the roller members; a plurality of transfer members arranged along the first direction between the roller members and spaced from one another so as to be enclosed by the endless belt; and a frame that rotatably supports the roller members and the transfer members. The frame includes: a pair of resin side frames spaced from each other in the second direction, each of the resin side frames extending in the first direction; and a resin bridging beam extending between the side frames.