In this study, the effect of land cover and thermally induced local circulation on convective precipitation in mountainous region around the Lake Biwa is investigated by numerical simulations. Firstly, numerical simulations, which have realistic land cover, are carried out on 15th Aug. 2001 (precipitation was observed around the Lake Biwa) and 14th Aug. 2001 (precipitation was not observed around the Lake Biwa) and it is found that both local circulation and atmospheric environment are important for the precipitation. Secondly, some numerical simulations which has imaginary land cover (forest is changed into paddy field) are carried out on 15th Aug. 2001 and it is found that transportation of water vapor by local circulation induced by heating from the land surface is more important for the precipitation than evaporation from the land surface.