This paper studies a design problem of the optimal buffer of a generalized conveyor-serviced production station (Generalized CSPS). The problem is first formulated as that of minimizing the sum of delay-and-overflow cost and buffer cost, with respect to the look-ahead interval, c_N, maximum in-process inventory N. Second, under a given planning period, T_0,it is found by simulation that the optimal buffers, c^*_N and N^*, exist when a design factor, ε, is 0&lnE;ε<1. Third, the behaviors of the optimal buffers are considered under some input parameters. Finally, a design procedure is given, and its introductory conditions and effects are numerically showed.