[en] In order to maintain and develop civilization in 21st century, the stable supply of energy based on long term viewpoint is indispensable. As to nuclear fusion, fuel exists widely and abundantly on the earth, it possesses high safety in the principle, and is superior for the protection of environment. The research and development of nuclear fusion reactors are at present at the stage of having attained the critical plasma condition, and the subjects to be solved for its practical use remain, accordingly hereafter, the further efforts of research are required. Japan Atomic Energy Research Institute has advanced the research and development for the practical use of nuclear fusion reactors conforming to the basic plan of third stage nuclear fusion research and development decided by the Atomic Energy Commission, and established the technologies at the top level in the world. The engineering design of the international thermonuclear fusion experimental reactor (ITER) is in progress by Japan, USA, EU and Russia. The way to nuclear fusion, the concept of nuclear fusion reactors, the confinement of high temperature plasma, the device of component machinery and equipment and others are described. (K.I.)