Relationships between submarine groundwater discharge (SGD) and the freshwater-saltwater interface are evaluated by continuous measurements of SGD rates, conductivity and temperature of SGD, and resistivity measurements across the coastal aquifer. Our measurements show that the processes of SGD differ between the offshore and nearshore environments. SGD and submarine fresh groundwater discharge (SFGD) rates were largest just landward of the saltwater-freshwater interface. SGD variations landward the saltwater-freshwater interface had negative correlations with tidal variations, because of the connections of terrestrial groundwater in the land and the ocean. SGD in the nearshore can be explained mainly by connections of terrestrial groundwater, while offshore SGD rate is controlled mostly by oceanic process such as recirculated saline groundwater discharge.