Japanese iriai forests have been regarded as a model of institutions for collective action in the sustainable use of resources in studies on commons, as pointed out by Ostrom (1990) and McKean (1996). However, present-day iriai forests that have survived decades of legal and even greater economic and social challenges have undergone significant alteration. While we know that external conditions such as foreign competition from low-cost timber have depressed the Japanese forestry industry and thus reduced the health of Japanese forests as a whole, we do not know about the current state of the iriai forests in particular. Adaptation to external impacts is crucial for the survival of the commons in a modern industrialized society. This study examines external impacts on traditional commons and the resultant institutional changes in current Japan. We cannot easily track the changes in traditional commons without deep understanding of many cases, because the factors affecting their functioning are complex and diverse. Therefore, we opted to use the case study method to improve the empirical foundations for analyzing these complex phenomena. Our goal was to examine the institutional changes resulting from one source of pressure found in many commons near urbanizing areas in postwar Japan – an increase in newcomers – as well as from the pressure of foreign competition in forest products. We chose eleven villages in the Yamaguni district in Kyoto city that manage their own common forests and studied the documented rules in these communities. We used participant observation and also conducted interviews with villagers to obtain their sense of change over time, the impact of globalization, and the current status of the commons. This paper derived the following conclusions. First, the village community can adapt its institutions to external influences by supporting continuous institutional change. Second, although village communities can overcome most external impacts themselves, there is one impact, low-priced competition due to free trade in forest products which they cannot cope with independently. Third, regenerating local Japanese commons requires multi-level governance based on the principle of subsidiarity.