One of the problems encountered in the design and implementation of a flexible transfer line (FTL) is the layout design of the FTL. The layout design of the FTL has an important impact on material handling. In this paper, we develop a LAyout Design system (LAD). LAD can find FTL layout design including the buffer size between each pair of FTL machine tools. LAD divides the goal plant into cells and uses GA to find the efficient FTL layout design. In order to carry out GA, we propose a new encoding method to express GA individual. The new encoding method is called a One by One Encoding Method (OOEM). OOEM generates the elements of the individual one by one with the sequence of relative direction of the FTL components. The sequence of individual elements indicates the sequence of machine tools and conveyer buffer spaces of FTL. The developed LAD based on the proposed OOEM is not limited to a single static environment plant, but is highly flexible within the plant structure. An application example was developed, and after a number of generations based on LAD, an efficient FTL layout design was able to be found.