In this paper, a design of the optimum buffer stocks in group-oriented flow line that has seen developed to eliminate the balance loss and the down of morale in common flow line is considered from the viewpoint of its effective application. As the result, a theory of the optimum buffer stocks that minimizes the loss is suggested based on the relations between the extent of eliminating the balance loss and the downs of the work efficiency by making buffer stocks. A theory that introduces this result relating to the spatial maximum stocks in each station is also suggested.