This paper develops an optimal manpower scheduling algorithm that gives an optimal workforce size and day-off scheduling required to satisfy following conditions. First, everyone is to have two consecutive day-off per cycle in a continuous operating environment. Second, everyone is to have at least A weekends off in a cycle of B Weeks. The model addressed is under the circumstance that the demands can vary from day to day in a weekly cycle. The proposed algorithm makes it possible to minimize the maximum workstretch and to maximize the number of weekends off. It is also possible to minimize the variance of idle manpower distribution in order that idle manpower may be utilized in case of emergency.