We analyze, using official data, the spatial mobility between three areas in Saitama Prefecture (Kawaguchi, Urawa and Omiya), and that from them to Tokyo. From this aspect we examine how these areas changed into the suburbs. It is usually thought that the suburbs are born into rural areas under influences of one city outside of them. But by these three areas the suburbs are born under influences not only of a large city but also of the local cities, and into such cities. Because they were cities, these three areas could offer many houses, through their urban planning and so on, to many newcomers' families and workers employed in the large city Tokyo, earlier than any other area around them. Because they were cities, they gathered people from neighborhood as much as they sent to Tokyo, and these flows of people have now amalgamated them into a new large city. These mean that the suburbs can be seen as the areas in which not only farmers and newcomers but also many other social classes different in previous residence, working place and occupation coexist and cooperate. This finding will be useful in solving the problems of human relations in the suburbs.