[en] One of the most important applications of nuclear fission and nuclear spallation is high performance neutron sources. The neutron sources mentioned here are those used for beam experiment in the research on material science and the basic physics of atomic nuclei and others. In the spallation neutron sources using medium energy proton accelerators, in the case of using nonactinide targets, nuclear fission takes part in addition to nuclear spallation, and in actinide system, nuclear fission and nuclear spallation coexist. The most important thing as high performance spallation neutron sources is that cold, thermal and epithermal neutron fluxes as high as possible can be obtained. As the spallation neutron source in Japan, KENS-1 was completed in 1980 for the first time in the world. KENS-2 is planned as a part of the Japanese Hadron Project. The optimization of a proton accelerator, the targets for generating neutrons, the coupling of a target with moderator, cold neutron sources and the distribution of proton pulses to a target, moderator and reflector assembly, and the new method of proton beam incidence are reported. (K.I.)