In minimizing the assembly schedule for job production of the large-sized product, when all operators can be charged with all the assembly process, a serial assembly system is available, but when all operators can be used but cannot necessarily be charged with all the assembly process, a minimum necessary parallel assembly system can be added. In a study of the ease where all operators cannot be used, the system with more operators in charge is more effective in a comparison between the straight and parallel assembly systems. While in a comparison between two parallel assembly systems, the one with higher balanced schedules is more effective.