空地等の発生動向や利活用に関わる課題は地区特性毎に異なるが，分散・細切れで発生し集約利用が困難であること，空地等を固定化させがちな地権者意識は共通課題である。空地等の利活用の今後の新たな一つの方向として，暫定利用が考えられる。暫定利用は空地等の増加・減少の両局面で，地区特性にあわせた利用が可能である。今後大きく危惧されるのは所有者不明土地の増加である。空地等の問題を考察することは，都市再編や今後の国土利用の検討につながる。

The fight against vacant houses （la lute contre le logement vacant） constitutes one of the priorities of the French law makers. The Government introduced the taxation on vacant houses, the requisition and a system of short term lease contract, to mobilize vacant properties to accommodate growing population. It enhances also measures against buildings threatening to collapse.

This paper analyzes the effect of current various countermeasures for external diseconomy caused by unmaintained vacant houses and buildings from the point of view of Law and Economics, and shows that such countermeasures do not necessarily function eff ectively and efficiently. As the result of these, this paper proposes to give appropriate incentive in tax system to owners of those houses and buildings as the direction of future countermeasures.

After the year 2018, an earthquake-resistant diagnosis will be imposed for old and large scaled buildings that are used for unspecified many people, and the result of diagnosis will be announced publicly. The rule of the law is that while a certain building is realized to be dangerous, this building is still completely legitimate. When a building is collapsed accidentally, this rule causes the dispute between the victims of an accident and building owners, because the victims say that this building is dangerous while the owners say this building is completely legitimate. In order not to cause unnecessary disputes, the law should be changed to make clear the ownerʼs responsibility to repair the dangerous building.

The purpose of this paper is to obtain new knowledge of change of Japanese land policies after World War Ⅱ. Therefore, we think land is an image, not an entity as usual, and introduce new concept of views of land. By content analysis of the documents of comprehensive land policy, Diet Minutes, etc, we found views of land had changed unidirectionally, in another words, there was one way expansion of the difference between land as entity and land as image.