Around a river mouth at open coastal zone, complicated flow fields arise from interactions between waves, tidal and fluvial currents. To estimate sediment budget around river mouth, it may be important to investigate the current field. In this study, spatio-temporal properties of the currents off the Tenryu River mouth on the Pacific Ocean are discussed based on field data and numerical simulation. The field data were obtained in five-year observation in summer from 2006 to 2010. The westward component is significant in the vertical profile of time-average current. The bottom layer currents are developed in long-term under the influence of a flood discharge. Also from the numerical simulation with 3D hydrodynamic model, seasonal variations of the current field in wide coastal area have been roughly reproduced.