Alternative energy sources such as solar, wind and geothermal energies in Japan have been developing in line with the national energy policy of Japan ever since the first worldwide oil crisis occurred in 1973. Japan is abundant in geothermal energy sources which will contribute to protect the global environment because of low emission of CO_2 in terms of power generation. The nationwide systematic surveys of geothermal resources have been carried out in the volcanic regions, particularly in Hokkaido, Tohoku and Kyushu by public and private sectors since 1973. Those activities for geothermal exploration led to the birth of new geothermal power plants in rapid succession, and the current geothermal power generation in Japan is 533MWe in total from 17 power stations which is the fifth place in total generation in the world. The geological data about volcanic fields, especially calderas and basement geology beneath the volcanic regions covered with younger sediments, have been integrated by the nationwide geothermal resources survey carried out by NEDO since 1980 through geological, geochemical and geophysical methods associated with drilling works. The small-scale calderas such as Nigorikawa (Hokkaido), Sunagohara and Hijiori (southern Tohoku) in Quaternary age were selected as the promising areas for geothermal exploitation. A funnel-shaped caldera with steep walls was discovered in Nigorikawa through the drilling by private sector. The Nigorikawa caldrea was defined as one of the most common Japanese caldreas. The large-scale volcanic fields in Tertiary to Quaternary time such as Hakkoda, Sengan (northern Tohoku), Kurikoma (southern Tohoku) and Hohi (Kyushu) have been also surveyed in detail for geothermal exploration. The schematic models of calderals or "volcano-tectonic depression" (VTD) named Okiura, Old Tamagawa, Pre-Yakeyama, Sanzugawa and Shishimuta were proposed in those fields. The Quaternary granitic body (Kakkonda granite) was founded at 2,860m deep below the surface in the Kakkonda (northern Tohoku) through a deep geothermal well drilling by NEDO. The bottom-hole temperature at 3,729m deep should be higher than 500℃ because pure metal tellurium with the melting point of 449℃ was fused at the bottom of well. These data shows the Kakonda granite could have a possibility of the geothermal heat sources in Kakkonda. The Quaternary active volcanoes like Akan (Hokkaido), Akita-yakeyama (northern Tohoku), Hachijo (central Honshu), Unzen and Kirishima (Kyushu) are quite hopeful for goethermal development. Exploration wells drilled into or around those volcanoes were mostly successful in getting steam and hydrothermal fluids. A lot of useful information concerning the Tertiary granite and basement geology covered with younger volcanic sediments in Sengan, Kurikoma and Hohi have been accumulated by the geothermal exploration survey. Geothermal reservoirs have been initially recognized to be porous-type media underlying cap rocks which are similar to petroleum reservoirs. But the recent exploration survey results show that fracture-type reservoirs consisting of complicated fractures and/or faults are more dominant in the exploited fields. The Ogiri and Yanaizu-nishiyama geothermal power stations exploited in the last five years are characterized by the fracture-type reservoirs consisting of vertical faults with steeper angles. It has been becoming clear worldwide that geothermal activities have close relation to the formation of hot spring-type gold deposits. Prospective gold mineralization containing several tens grams Au per ton have been discovered in the fracture-dominated parts developed along the marginal zones of "cauldron" in the Hohi geothermal field by the surveys of MMAJ for the past more than ten years.