In a method of manufacturing an electrode assembly for a rectangular battery, in which positive electrodes and negative electrodes are alternately laminated so that a separator exists between the respective positive and negative electrodes, the manufacturing method includes the steps of: arranging a plurality of guide members in zigzag form in a perpendicular direction; inserting a continuous member of the separator between one and another one rows of the guide members; folding, into zigzag form, the continuous member by intersecting the rows of the guide members in a horizontal direction; inserting alternately the positive electrodes and the negative electrodes in respective valley grooves of the zigzag-folded continuous member; withdrawing the guide members from the respective valley grooves of the continuous member; and pressing, thereafter, the continuous member in the zigzag direction so as to make flat the continuous member.