A battery module comprising: a stack comprising a plurality of battery cells, each of the battery cells comprising a case and an electrode member contained in the case; a fitting portion comprising at least one of a concave portion or a convex portion formed on a stack surface of each of the battery cells of the stack, wherein the stack comprises: a separator formed of an insulating material and interposed between adjacent ones of the battery cells, the separator comprising: (i) a convex portion which is formed on a joining surface in contact with one of the battery cells and is fitted with the concave portion of the fitting portion, or (ii) a concave portion which is fitted with the convex portion of the fitting portion, the fitting portion positioning and coupling adjacent ones of the battery cells to the separator; a first frame which is fitted with one side surface of the stack and constrains the battery cells in a stacking direction; a second frame which is fitted with another side surface of the stack and constrains the battery cells in the stacking direction; and press members located at respective ends of the stack and connected to the first frame and the second frame, the press members being configured to generate an urging force for pressing the electrode members of the battery cells from outside the battery cells, and wherein the press members are rectangular and have the same size as a surface of the battery cell opposed thereto, and have a curved portion having a concave portion which is depressed at the centre thereof toward the battery cell, the press members further comprising legs provided on the periphery of the curved portion and that are brought into contact with the surface of the battery cell. a stack comprising a plurality of battery cells, each of the battery cells comprising a case and an electrode member contained in the case; a fitting portion comprising at least one of a concave portion or a convex portion formed on a stack surface of each of the battery cells of the stack, wherein the stack comprises: a separator formed of an insulating material and interposed between adjacent ones of the battery cells, the separator comprising: (i) a convex portion which is formed on a joining surface in contact with one of the battery cells and is fitted with the concave portion of the fitting portion, or (ii) a concave portion which is fitted with the convex portion of the fitting portion, the fitting portion positioning and coupling adjacent ones of the battery cells to the separator; (i) a convex portion which is formed on a joining surface in contact with one of the battery cells and is fitted with the concave portion of the fitting portion, or (ii) a concave portion which is fitted with the convex portion of the fitting portion, a first frame which is fitted with one side surface of the stack and constrains the battery cells in a stacking direction; a second frame which is fitted with another side surface of the stack and constrains the battery cells in the stacking direction; and press members located at respective ends of the stack and connected to the first frame and the second frame, the press members being configured to generate an urging force for pressing the electrode members of the battery cells from outside the battery cells, and wherein the press members are rectangular and have the same size as a surface of the battery cell opposed thereto, and have a curved portion having a concave portion which is depressed at the centre thereof toward the battery cell, the press members further comprising legs provided on the periphery of the curved portion and that are brought into contact with the surface of the battery cell.