This report surveys potential impacts of ASEAN (Association of South East Asian Nations) on inter-ASEAN affairs and its external relations when ASEAN will enlarge its members to include all nations in South East Asia, and thus fully represent the region. For this purpose, the survey was conducted on Vietnam, Myanmar, Laos and Cambodia, which joined in 1995, from the viewpoint of their economic and political system, and their relations with other member countries. The nature of ASEAN has gradually transformed, in which all the countries in the region have increased and internal economic issues have been tackled. It has an aim to stimulate inter-ASEAN trade and induce foreign direct investment into ASEAN as a whole by reducing import duties on intra-ASEAN trade. Underlying in these, new development is a concern about growing economic and military power of China. ASEAN solidarity will work an leverage against China should change toward worse, and ASEAN will function as a regional stabilization factor. ASEAN is needed for the stability of both in economic and political order in East Asia. Japan has to further promote its cooperation with ASEAN to help its solidarity as an association. 24 refs., 21 figs., 25 tabs.