A producing method of an assembled battery includes: preparing plural battery cells each of which includes an electrode body having a positive electrode and a negative electrode, and a container for housing the electrode body; classifying the plural battery cells into plural thickness ranks depending on a thickness in an arrangement direction of the electrode body housed inside each battery cell; and arranging the plural battery cells in the arrangement direction, and fastening the plural battery cells such that a load is applied to the plural battery cells in the arrangement direction, the plural battery cells being selected from the plural thickness ranks in a manner as to conform a length in the arrangement direction of the battery cells is adapted to a predetermined length when the plural battery cells are arranged in the arrangement direction.