We know that Japan is facing a declining population and an aging society. And we recognize that the social situation thirty years later will be entirely different from today. Nevertheless many local municipalities have maintained concepts of growth paths for cities predicated upon expansion of the population, and the delay in responding to the declining population is serious. It is by no means easy to make a 180-degree turn. But it is necessary for us to remember that there is only a limited amount of time in which to address this issue. This paper aims to propose that many municipalities should promote the reduction of the size of urban areas in line with population decline and the restructuring of infrastructures in urban planning as soon as possible. While doing so, announcing details of implementation plans with a timeline encourages residents to change their place of residence and encourages the flow of private investment into the new urban area.