[en] The development of high temperature gas-cooled reactors has very important significance for the energy policy of Japan to diversify energy sources and stably ensure energy. The development has been advanced since 1969 by Japan Atomic Energy Research Institute, but in the 'Long term plan of atomic energy development and utilization' of June, 1987, as high temperature engineering test and research, it was decided to construct a High Temperature Engineering Test Reactor (HTTR). According to this policy, JAERI carried out the detailed design and safety analysis of the HTTR with 30 MWt output and reactor exit coolant temperature of 950degC. The application for the permission to construct the HTTR in Oarai Research Establishment was made in February, 1989, and it is expected to begin the construction in 1990. The period of the construction requires about 5 years, and the criticality is scheduled in 1995. In JAERI, the high temperature engineering test and research including the utilization of the HTTR and the heightening of temperature in high temperature gas-cooled reactors are promoted. The trend of development of high temperature gas-cooled reactors in foreign countries and the research activities in JAERI are reported. (K.I.)