We develop the system to decide the efficient layout of assembly production line by using Genetic Algorithm (GA). We call the system as Decision System of Plural Production-lines-layout by GA (PPG). PPG decides the efficient layout of production line by using GA, work-flow-line acquired by Chameleon code and the machine breakdown data. PPG evaluates the layout efficiency by calculating the operator’s walking time to fix the machine breakdown occurred on the production line. By the evaluation, it is ascertained that PPG was useful.