The first highway in Japan was opened in July 1963 between Ritto and Amagasaki with the length of 71km. The total length of highway in Japan reached 7, 236km in August 2003. The highway construction has become a crucial issue in the recent Government reformation under the sever conditions of Japanese economy and national finance. However, the provision of highway brings about various positive economic effects in the surrounding areas, such as the new location of industries, the rationalization of distribution systems, the promotion of tourism and the improvement of living conditions. It is obvious that the rapid growth of Japanese economy has been supported by the construction of highway network since 1960s. Therefore, a long-term impact analysis, which considers the changes in regional economic structures, passenger flows and commodity flows, is necessary to identify the exact outcome of highway construction projects. This paper aims to examine the long-term impact of highway network construction on the travel time between 46 prefectures in Japan and their effect on the inter-prefectural commodity flows. The outcomes of highway network provision have been measured with the changes in the shortest travel time by car between prefectures and the surplus for commodity flows induced by the improvement of travel time. The empirical study has been conducted for years 1975-2000. The main findings have revealed that the trunk highway construction during 1975-80 had brought about a significant improvement of travel time and surplus for commodity flows in the metropolitan regions. The improvement in local regions appeared after 1980s. The highest improvement for commodity flows had been achieved between 1995 and 2000 when the local highways connected to the trunk network. The fact has revealed that the formation of highway network in local regions is effective to improve the conditions of commodity flow in the whole nation.