Recently, the maintenance of the road structures such as bridges has been important both in the developed countries and in the developing countries. For the maintenance of road structures, it is important to investigate on the service conditions including the weights of vehicles and the number of vehicles. For that purpose, Weigh-in-Motion is one of the promising methods, but in the developing countries, it is difficult to prepare adequate equipments to perform the existing highly accurate Weigh-in-Motion method. In this paper, attempts to develop portable Weigh-in-Motion with a simple portable measurement system and simplified data interpretation for field measurements were described.