A bus bar assembly structure includes an electrode terminal and a plate-shaped bus bar that is assembled to the electrode terminal. The bus bar has a burr along an edge of one of openings of an insertion hole. A threaded portion of a nut has a tapered portion at an edge of one of openings of the threaded portion, and a largest diameter of the tapered portion is greater than a bore diameter of the insertion hole. A flat portion of the bus bar is held between a bolt and a nut while the burr is located within a space created by the tapered portion.