In the Marugame plain, recent variation in the hydrologic cycle due to landuse change has posed urgent need to develop new water resources in harmony with the sustainable water cycle. In this paper, measurement of confined and unconfined groundwater and data collection of water uses in the plain were carried out and a numerical analysis of the hydrologic processes for five years including dry and wet years was performed using the MIKE-SHE model, with special emphasis on agricultural water use. It was made clear that the numerical model can fairly reproduce the daily river discharge of the Doki River and the groundwater levels in the plain. And water balance analysis for 1996 showed that the evapotranspiration accounted three-quarters of the annual precipitation and that the domestic water use is heavily dependent on the groundwater and the water introduced through the Kagawa water conveyance channel.