A new quantitative index for construction investment is desirable from the viewpoint of the amount of structures which have been constructed to discuss on construction investment. The regional difference in the amount of construction investment in Japan was considered through the consumption of ready-mixed concrete in each prefecture of Japan in the year of 2000. The author employed the consumption of ready-mixed concrete as a simple and clear quantitative index for the amount of structures, in addition to the conventional indices for construction investment indicated with money. The consumption of ready-mixed concrete was divided into for private and public uses. It was found that the relationship between the population of each prefecture and its consumption of ready-mixed concrete for private use was almost proportional. That can be reflected by the construction demand for private use mostly generated from the population only. On the other hand, it was found that the relationship between the population of each prefecture and its consumption of ready-mixed concrete for public use was not proportional and that the smaller population corresponded to the larger consumption of ready-mixed concrete per capita. It can be concluded that some amount of construction investment for public use is indispensable despite of the population from the viewpoint of development of infrastructure.