Abstract In Japan, there are about twenty geothermal areas, where heat is transferred by various processes, such as fumaroles, steam wells, hot springs, steaming grounds, evaporation from hot pools and thermal conduction through the earth. In this paper, our methods of heat transfer measurement which have been used at Owakudani and Sounzan geothermal areas of Hakone Volcano are outlined. Total mass discharge from these areas amounts to 129 kg/sec and total heat transfer amounts to 10.64 · 10 6 cal./sec which is equivalent to 1 · 10 22 erg/year, corresponding to a moderate volcanic eruption a year. Assuming that the geothermal areas of Japan have the same scale as Owakudani and Sounzan areas put together, heat transferred from all geothermal areas of Japan may be estimated roughly to be 2 · 10 23 erg/year. Adding to this, the energy 7 · 10 23 erg/year released by the volcanic activity, 1.1 · 10 24 erg/year by the common hot springs, and 7.3 · 10 24 erg/year by the normal heat flow of non-volcanic regions, we can estimate the total energy released from the whole of Japan, exclusive of that by earthquakes, to be about 9 · 10 24 erg/year.