To provide an assembly type bus duct whose assembly is easy and which can reduce damage of an insulating conductor when a case (box) storing the insulating conductor is attached to the long insulating conductor and to provide a bus duct box.

The bus duct box includes a lower plate member having a flat bottom portion, a lower vertical face portion which is integrally formed at a right angle with the bottom portion, a lower engaging portion arranged in the lower vertical face portion; and a connection lower plate material formed of a flat plate material connected to one end in a longitudinal direction of the bottom portion; and an upper plate member having a flat upper face portion, an upper vertical face portion which is integrally formed at the right angle with the upper face portion, an upper engaging portion disposed in a part corresponding to the lower engaging portion in the upper vertical face portion, and a connection upper plate material which is connected to an outer surface of an end in the longitudinal direction of the upper face portion and the upper vertical face portion. The lower plate member and the upper plate member are combined facing each other. An inner surface of the upper vertical face portion of the upper plate member is overlapped with an outer surface of the lower vertical face portion of the lower plate member to assemble the bus duct box.