To provide a bus duct which achieves its elongation by adding a box of the bus duct in an optional position without using a welding method or a patch.

A bus duct, in which boxes having U-shapes in cross sections are joined together to face each other and which accommodates a plurality of conductors in the space formed by the boxes, is equipped with: a first box piece, in which the plurality of boxes are arranged via first specified joints in the longitudinal direction of the bus duct; and a second box piece, which is joined to face the first box piece and in which the plurality of boxes are arranged via second specified joints in the longitudinal direction of the bus duct, and the first joints and the second joints are formed at a specified interval in the longitudinal direction of the bus duct.