In the forth report of this research, we investigated the optimum design method for the material handling system of seaport container terminals. The focus was on the optimum layout and operation, with fluctuation of handling volume and interference of handling equipment in sight. In the previous three reports, we analyzed the processing time and the essential number of equipment usits on shipping, receiving and delivery operations for every handling system of the transfer crane and straddle carrier. We, also analyzed in this forth report the fluctuation of the handling volume in the terminal and took into account the effect of the enlargement of container ships. Further more, we considered the handling ability, and found the connection of land availability, annual cycling rate of container terminals and the handling system. We derived from the relationship between the interference of straddle carriers and operational time, that an ultimate number of handling containers exists.