A method for manufacturing an electrode assembly includes a unit cell grasping step of moving a movable gripper to grasp a unit cell having an electrode and a separator, a vision measurement step of vision-measuring a full width value of the unit cell, and an input step of determining a width difference between the full width value of the unit cell and a set width value stored in a memory, and moving the unit cell by the movable gripper while taking into account the width difference to seat the unit cell on the separation film. A method for manufacturing a secondary battery includes a manufacturing step of manufacturing an electrode assembly according to the above, and an accommodation step of accommodating the folded electrode assembly in a battery case.